Ever been sick of getting focused and melted in teamfights? Ever wished you could make your opponents stop attacking your AD Carry? Ever wanted to make that silly Master Yi kill himself? All these things are possible with Rammus, the Impenetrable Wrecking Ball, and I'm here to show you how it's done! (Or do my best trying). I have moderate experience with Rammus, and have been largely successful in using this armordillo's abilities to help my team win games. As Rammus, you are NOT the primary damage dealer, although you should be enough of a threat that you cannot be ignored (as if your taunt wouldn't accomplish this task already!) Without further ado, let's go into the nuts and bolts of how this champion works!

Pros and Cons of Rammus:

Pros:

Excellent Crowd Control. THREE SECOND TAUNT. THREE SECONDS.
Very difficult to kill if played correctly. Defensive Ball Curl is a built-in defense steroid to repel harassment.
Tremors is on a short cooldown, and carries the ability to damage towers.
Powerball is one of the strongest initiation spells in the game, giving rammus excellent mvoement speed and slowing his opponent on contact.
Very strong ganks both before and after level 6.

Cons:

Farm Reliant. Rammus does not do well if he cannot enhance his abilities with items.
Susceptible to ranged harass. Rammus does not have sustain and can be knocked off his last hitting if he doesn't get a good lane.
Not really the best farmer in the game, given that he builds primarily defensively and only has melee range.
As with many other champions, he is susceptible to crowd control. If the enemy team can stun him before he initiates, your team may be in deep trouble for the upcoming teamfight.

For runes, I like to take semi-standard jungling runes. I start with nine Greater Mark of Desolation for the armor penetration that makes your early auto-attacks a bit stronger and makes jungling/last-hitting easier if you decide to go that route. However, the Greater Mark of Magic Penetration also does well for mid-late game as it helps your Defensive Ball Curl and Soaring Slam deal more damage, as well as that Sunfire Aegis and Thornmail damage you may be picking up if the enemy team is heavy in physical damage.

For Seals, I believe that Greater Seal of Armor are the only way to go with Rammus. While it's possible that the Greater Seal of Defense may provide you with stronger armor in later levels, the early bonus flat armor provides you with easier jungling capability and the combination with Spiked Shell for early-game damage helps significantly. You can always buy armor later in the game, and early game is where runes enhance the most.

For Glyphs, since you don't need flat MR for jungling and mages aren't especially dangerous until their skills have leveled up a bit, I find that Greater Glyph of Scaling Magic Resist are the strongest rune available. At level 10, these break even with the flat MR glyphs, and thus will be more helpful in the teamfighting phase.

Quintessences are a bit more of a wide-open option, but I personally prefer the flat health afforded by Greater Quintessence of Health. As Rammus, there really isn't a reason to go for many of the "utility" quintessence options: Movespeed won't help much when your powerball lets you chase down nearly anything in the game, gold/10 is not going to grant you enough money to be noticeable (seeing as you're farming jungle creeps and/or lane minions), and experience gain quintessences won't net you enough of an advantage to be worthwhile. However, I have seen the flat armor provided by Greater Quintessence of Armor do well to grant an extra bit of oomph into your early game last-hitting and defenses.

Masteries are a fairly straight-forward 0/21/9 tree. I like to grab any and all damage mitigation options in the defensive tree, beginning with all three levels in both Resistance and Hardiness . I also like the Tough Skin mastery for the access it gives to Bladed Armor , which allows Rammus to jungle a little bit easier (as well as having excellent synergy with Defensive Ball Curl. If you plan on jungling at all, the point in Summoner's Resolve is worth it for the extra gold on smite. Nobody ever had trouble with getting more money, right? Due to having more health and Rammus's natural defenses, I also really like taking all four points in Durability and the then-unlocked point into Veteran's Scars , which grant you some significant HP bonuses to keep yourself alive. Depending on Whether or not I'm jungling, I take 2 or 3 points into Initiator for that little bit of extra movement speed to ensure your Powerball isn't outrun. I always take all three points in Honor Guard more for the novelty of percentage reduction than anything else, and I finish off the defensive tree by grabbing the point in Juggernaut for further survival ability and crowd-control reduction.

In the Utility tree, I take all three points in Good Hands to facilitate faster return to the battlefield in the event of my death (Rammus IS a tank, so expect to die with him for the good of your team!) Other options in the utility tree are not as important, save for the point in Runic Affinity if you intend to jungle. The speed afforded by Swiftness is helpful but not necessary, similar to the option of putting points into Expanded Mind and perhaps Scout (if you're jungling, you should be placing wards). Missing the spec on Ghost is the only noticeable downside to this mastery tree, and it rarely matters if you're using your Powerball to chase/initiate/get into range anyway.

Really, almost anything goes, but I find that one of either Ghost or Flash is essential to his success.

Top Tier choices:

Ghost: Helps you chase, flee, initiate, and pretty much just go wherever you want to as Rammus. Combined with Powerball, crossing the map is nearly as fast as the Teleport summoner spell while having many more uses.

Flash: Flash gives a few tricks up your sleeve that ghost does not, and gives you even more in combination with ghost. Flash is mostly used to go around things that you otherwise might not be able to, such as walls in the jungle and creeps. One of the oldest tricks in the book for Rammus players with flash is to Powerball up to a minion wave (or enemy team) and use flash to instantly close the distance, giving the AoE slow to the team before they were prepared for it (or, in some cases, to manage to hit that Annie or Kog'Maw hiding in the back of the team). Use Flash to put yourself in prime positioning for Puncturing Taunt at the start of a teamfight.

Smite: A Fantastic, must-have spell if you intend to jungle as Rammus. Keeps your buffs from getting stolen, speeds up your jungling route, and gives you more money. However, outside of jungling, this summoner spell has almost no use.

Exhaust: A good summoner spell to take, but rarely is Rammus the champion who should have it. While it grants you the ability to carry an extra disable outside your taunt, it removes one of the previous summoner spells mentioned.

The rest of these, I find far less useful on Rammus, but still can serve some good:

Ignite: Allows you to finish off a very low-health opponent without chasing, does true damage to tanks, and stops healing-dependent characters (think Dr. Mundo and Volibear). However, as with Exhaust, this is yet another spell better taken by somebody else on your team.

Heal: A fairly strong choice as it grants you another huge chunk of HP that makes your heavily stacked resistances seem even more impenetrable, but grants you nothing offensively in a teamfight.

Teleport: On Rammus, ghost does nearly everything this spell can do, but with more versatility. That being said, it can still be nice to save a tower from a heavily pushed wave when necessary.

Cleanse: with Season 2's buff of this summoner spell, it can be useful, but you already have fairly strong CC reduction between the Juggernaut Mastery and Mercury's Treads, so its use is, again, greatly diminished.

Clairvoyance: If nobody else on the team has it, you can consider getting it, but this is honestly a spell that somebody else can use better than Rammus can.

And these are the summoner spells I consider bottom-tier (almost 100% useless) with Rammus:

Surge: What bonus does a tank really get from having more ability power and attack speed?

Revive: While the ability to get yourself right back into battle might seem nice, usually by the time you can return to a fight, it's over regardless of your respawn timer. Niche use, I find others to be far more effective.

Promote: Rammus can push towers with his Soaring Slam and is already a tank, so promote would see nearly no use on him.

Clarity: Rammus can deal with mana problems using either blue buff or Chalice of Harmony, and clarity really seems useless when he's not a spammy character to begin with.

Rammus is a tank that excels in damage mitigation and crowd control. I have selected skills in this order according to these roles.

Spiked Shell (innate): Rammus gains Attack Damage equal to 25% of his Armor.

More information: This skill is what allows Rammus to actually deal damage without building any damage items, as well as why Rammus players prefer to gain more armor before getting more magic resist given the option. However, this will not inherently turn Rammus into an AD carry, nor will it mean that stacking 500 armor against a mage-heavy team is a good idea.

Powerball (Q): Rammus accelerates in a ball towards his enemies, dealing 100/150/200/250/300 (+1 per Ability Power) magic damage to nearby enemies on impact and slowing them by 20/25/30/35/40% for 3 seconds.
Mana Cost: 80/90/100/110/120
Cooldown: 10 seconds

More Information: This is Rammus's initiation, chasing, and fleeing skill. Proper use enables Rammus to perform VERY strong ganks, lets him close the gap between himself and an opponent, and makes his taunt much easier to pull off. However, it is a bit of a mana hog and should only be used when necessary (i.e., not used to attack minion waves or jungle camps unless you have blue buff). Proper use of Powerball separates novice Rammus players from expert ones. I take a level in Powerball at level 2 and max it last.

Defensive Ball Curl (W): Rammus goes into a defensive formation for 6 seconds, increasing his Armor and Magic Resist by 50/75/100/125/150 and returning 20/30/40/50/60 (+10% of armor ) magic damage to attackers.
Mana Cost: 50
Cooldown: 14 seconds

More Information: This is the skill that allows Rammus to jungle, as well as the one that makes him a tank. Without this huge buff to his resistances, Rammus wouldn't be nearly as formidable. The return damage from Defensive Ball Curl and Thornmail will stack, as well, giving him a ridiculous amount of return damage that punishes auto-attackers for even thinking about killing Rammus. However, this skill should not be activated too early, lest it run out before the fight's damage burst has ended. I take levels in Defensive Ball Curl at level 1 and 3, and max it second.

Puncturing Taunt (E): Rammus taunts the unit into a reckless assault, reducing their Armor by 10/15/20/25/30 and forcing them to attack Rammus for 1/1.5/2/2.5/3 second(s).
Mana Cost: 50/60/70/80/90
Cooldown: 12 seconds

More information: This is Rammus's true bread and butter skill. with this bad boy, he can forcibly remove focus from his damage-dealing carries and literally drag melee champions should he desire. More commonly, however, it is used to force a champion into auto-attacking him and eating return damage from Defensive Ball Curl as well as allowing his team to focus the selected target into oblivion before they can escape due to the Armor reduction. In teamfights, use this skill to take out the highest-priority target, usually an AP caster or a fed AD carry. If their highest damage source cannot do what it wants, your team is that much closer to victory. I take this skill starting at level 4 and max it immediately. Occasionally, this skill is good enough that I begin taking it at 3, leaving the second point in Defensive Ball Curl for a bit later.

Soaring Slam (R) ("Ultimate"): Rammus creates tremors beneath him, dealing 65/130/195 (+0.3 per Ability Power) magic damage every second to nearby units and structures for 8 seconds.
Mana Cost: 120
Cooldown: 60 seconds

More Information: I personally love this ultimate and find it to be one of the most useful ultimate abilities in the game. On a short cooldown, it can be used to clear minion waves that are pushing a tower, tower-diving and killing towers (it damages buildings too!), or simply to enhance the Sunfire Aegis damage to reach 100/165/230 magic damage per second combined to everything that just happens to be near you. Add to that an eight-second duration, and your presence in a fight becomes very threatening. Take this skill every time it comes up at 6, 11, and 16.

"Quick Order" for skills:
R > E > W > Q (but don't entirely neglect W/Q early!)

There are only two items I consider truly "Core" for Rammus, and everything else can come afterwards depending on how the game is going.

First, the Mercury's Treads: Perhaps the greatest boots in the game at this point in time, although they may be rivaled soon by the new update to Ninja Tabi. Mercury Treads are expensive boots, but are worth every gold spent on them. Magic Resist is nice against mages, but the true winner is the tenacity these boots provide: nearly every crowd control effect is reduced by more than 1/3 of its original time with these bad boys.

Secondly, I love the Sunfire Aegis on Rammus, so long as the Giant's Belt component is purchased first. Rammus desperately needs the HP provided by the belt in the early-game, so I would recommend waiting on the Chain Vest component of the cape even if you have enough for it but not the belt yet. There have been too many times that I have died by taking the extra armor before I grabbed any Health. While some may argue that the recipe price for sunfire is expensive, I find the passive to synergize too well with his other abilities to pass up.

After that, several other viable options are out there, but are really dependent upon the strongest enemy damage sources.

Items Rammus does well with for Physical Damage:
Thornmail: Works incredibly well with Defensive Ball Curl at mitigating damage (max rank of DBC + this bad boy alone are a 71.43% damage reduction), and the damage returned from Thornmail is returned BEFORE mitigation. That means that, disregarding the magic resist the opponent has, you are sending back more damage than you are receiving with 250 or more armor.

Randuin's Omen: Works well with tremors and its active gets buffed by Defensive Ball Curl to add an immediate 1.5 seconds to the slow without factoring in armor and magic resist items Rammus may already have built. The active on this, used correctly, can keep enemy teams from being able to flee your team until it is too late. However, it is an expensive item and I prefer to save it for later in the game as such.

Guardian Angel: As if it weren't bad enough that Rammus has ridiculous resistances, imagine the ability to run into a battle and not die, even if they manage to eat all your health away! I really like the Guardian Angel as a last item on Rammus, but it's rare I get the oppportunity to build one before the game is over.

Items Rammus does well with for Magical Damage:

Banshee's Veil: Perhaps the most powerful single defensive item in the game, Banshee's veil provides a wonderful spell shield and a strong 50 magic resist when that spell shield is down. Also, it provides more health and mana, and Rammus loves having both of those to play with.

Force of Nature: 76 Magic Resist gives it the highest anti-magic power in the game. 8% movement speed means even without Powerball you're one of the fastest around. The health regen passive is a nice touch, but won't justify this purchase on its own. Grab it if you've got a banshee's veil but the enemy team is still pressing a lot of Magic Damage on you.

Chalice of Harmony: A good item to take early game, especially if you aren't getting blue buff and are having some mana problems. Also a fantastic "starter" Magic Resist choice if the enemy team composition makes Ninja Tabi a more attractive option.

Items that CAN Work on Rammus, but only see rare use:

Atma's Impaler: Yes, this item grants you more attack damage without "sacrificing defensive stats", but Rammus is not an offtank and my build doesn't afford rammus with a lot of HP to make this item really work well without additional investment. Still, if you're walking all over an enemy team, this can be a fun item to make the matchup even more lopsided.

Warmog's Armor: I will get this item occasionally if I feel that I've stacked up more resistance than I really need and think that the extra HP will make me nigh unkillable, but I still prefer stacking armor/resistances on Rammus in 90% of cases.

Wit's End: Perhaps the most underrated item in the game, Wit's End provides a nice magic damage bonus, a good attack speed bonus, and a stacking magic resist buff. At full stacks (four auto-attacks), it provides the same magic resist as a banshee's veil and is worth considering, but is overall much less useful as Rammus doesn't get a lot of auto-attacking time.

Frozen Mallet: Falls a lot into the same vein as Warmog's, although I find it even less useful. The slow on-hit is nice, but you've already got a built-in slow and the stacking of HP is better served with a Warmog's Armor anyway, which I've already covered.

Wriggle's Lantern: If you're jungling Rammus, I suppose you could consider this for the faster jungle clear, but too many of the stats it gives are too useless to really make it a strong choice on rammus. However, there are times and places where this works well on a jungling build to help secure dragon kills easier.

Aegis of the Legion: A nice early-game aura item that improves all of Rammus's Defensive stats. If you're going to get it, though, you'll have to do so before you finish your Sunfire Aegis or it's going to seem far less useful. Still a solid choice for jungling rammus and helps out your allies who don't build defensive in teamfights.

Nearly any other item I would /not/ suggest on Rammus under any circumstances.

Rammus is a team-reliant champion. That means you shouldn't be charging into the action all by yourself and expecting to win (or even come out healthy). However, with some teamwork, Rammus can drastically change the game. A Rammus gank consists primarly of the following:

Powerball in, preferably between your opponent and his escape, hit them to slow, immediately taunt, then activate defensive ball curl. If your team/lane that you are ganking gets in on this action, then a kill is nearly always ensured, unless the opponent is tower hugging and/or is able to flash to escape. However, remember the long cooldown on flash, over four entire minutes, leaves that opponent susceptible to a more aggressive gank in the near future.

In teamfights, Rammus's play changes only slightly. Target selection is still important, and it is up to you to tell your team who to focus if they're not doing it properly. Remember in this case that a little bit of consideration goes a long way. Yelling at your team for doing something wrong does not make them want to help you, but providing suggestions for them to do so often brings about positive results.

That being said, General targeting priority with Rammus is as follows: AP Nuker (if they aren't on cooldowns), Supports, AD carries are all priority number one, but probably in that order. AP Nukers are useless once taunted, so their entire damage capability can be removed with a good taunt + focus. Supports are generally pretty easy to kill in relation to their effect on the enemy team (nobody likes it when Soraka provides 800+ health to their AD carry along with some armor and silences your AP carry). AD carries are the next logical choice as they deal heavy damage, but are often hiding in the back. Grab the AD carry if they are able to start melting your AD carry, but otherwise leave them for after the nuker (and possibly support) is dead unless said carry is fed. Finally, the last ones to be targets are, 95% of the time, the tanks and off-tanks. Generally the ratio of their damage threat to their survivability is far too low for them to be important targets, but they should be cleaned up if at all possible at the end. You're doing something wrong if their tank dies but the rest of their team kills yours.

Generally, you want to be the one to die if somebody has to. That does not mean charging into fights without your allies nearby, but it does mean sticking around at low health if it gives your AD carry a few extra shots before having to retreat. Remember that you're best at taking damage, and make decisions for your team accordingly.

In Conclusion, Rammus is one of the strongest tanks in the game with a strong ability to focus on damage mitigation rather than HP increase, with a very good ability to pull damage off of his team's strongest damage source. In addition, his Tremors allows him to drop turrets with relative ease, making tower-diving less of a gamble for Rammus players. However, Rammus is not invincible and is especially weak without his Defensive Ball Curl. Furthermore, Rammus is at his strongest when he is able to gather up large amounts of farm, which is more difficult when dealing with ranged harass. All in all, he is a strong choice at any level of play, and can often help carry a team to victory through death.