Hey there, Welcome to my Mordekaiser 5v5/3v3/Dominion Guide. I build very similar in all the games I play, and I have only recently started using Mordekaiser again, but I seem to do pretty well.

I focus on a Tanky, long lasting Morde, with good anti-carry burst, and decent sustained AoE Dmg. This is a TANK BUILD, but with Sunfire Cape, and some 150 AP, your Dmg will be pretty good.

You can 1v1 almost anyone, I can't think of any real exceptions except maybe a super-feed enemy (But they would need to be able to soak up a lot of dmg, Maybe Udyr). It's easy to feel like you can't die and begin taking unnecessary risks (I know I have). Just make sure you have your team behind you, or your map indicates their team cant help them before attacking some one late game.

Also, should you be confused at any terms used in this guide, please reference the "Terms" Chapter or leave a comment.

Pros:
High Survivability
Can initiate team fights without worrying about dying
High Sustained Damage
Burst! (For those pesky nukes/squishies)
Extra Armor+MR [Creeping Death] On you or a teammate
Lots of health Early Game (7 Bar start + 2 Giant's Belt Items)

Cons:
Early Game, Abilities drain your health. Often spend a good amount on health pots to maintain laining (Hp/5 runes or an early [Regrowth Pendant] can help)
Weakened against heavy CC (Can be solved with [Merc treads] or [Moonflair Spellblade])

In 5v5:

Solo Top/Mid - You last hit minions and farm on up. You harass with "E" [Siphon of Destruction] and hopefully force your opposing lane to go back to base repeatedly. Also snagging some kills can help you, and your Team's Moral. If the other team has a jungler, a ward is a definite must for your return trips.

Group Laning - Let your partner get most of the Creep Kills, as they will probably benefit from it more. Still Harass with E, still ward if necessary (Buy one so your partner can save their money), and still snag those Kills/Assists.

Late Game - Initiate. Verbally keep the group on track. You are the leader and you should focus on keeping your team from wandering apart (That's more important then farming, organization means everything) Feel free to run in and soak up all their Cooldowns, and put a hurting on there team while you're at it, assuming your team is with you.

With your Ghost, you can easily reach the Squishier champions hiding in the back. The combination of Sunfire Cape + Creeping Death (on yourself) With your Q+E can help do solid damage to everyone around you. When you add your Ult + Ignite, it should be enough to overwhelm them a lot of the time.

Early Game it may be best to Auto-Attack instead of using your abilities. Depending on whether you want to push your lane, or let it be pushed, you should control you aoe dmg. This helps protect you from ganks, and puts less strain on your health. Morde has plenty of AD off the bat, you should be able to last hit fairly easy without abilities.

Picking up some quick nuetral creep kills in the jungle while your moving about can help keep your farming up.

Ult [Children of the Grave] - Packs a punch, and heals you up nicely. The range on this ability is crazy good, it's a sure-hit. The additional unit you recieve if the target dies with your ult on is just icing on the cake. It can be a VERY powerful force, especially if the person was a fed ad ranged. They can push towers quickly, burn enemies, last hit minions, scout around, and are just amazingly good. The ult is already something without this effect, and it becomes all the more valuable with it.

"E" [Siphon of Destruction] - Has been used to finish off the escaping champion more times then you can take a swing at, this ability has great range. The effect range of this ability is slightly larger then the animation would seem, so feel free to try using it even when it might appear your enemy is barely beyond your reach.

You've got plenty of options here. The goal of runes is to keep you Immortal, so MR/Armor is great.

For Marks I suggest Mark Of Insight Runes (Magic Pen), It will help you harass, and it's a standard.

For Seals I suggest Greater Seal Of Resillence (Flat Armor), although Health Regen and Health Regen Per Level Runes are also viable.

For Glyphs I suggest Greater Glyph Of Potency (Flat AP) As you won't get much AP till late, late game (Rylai's Is about it). Although MR and MR Per Level Runes may be used here if you are going to get some AP items early game (Such As Hextech Revolver).

For Quintessences I suggest Greater Quintessence of Potency (Flat AP) for the same reason as the Glyphs, it will give you a nice 25 AP to start the game off with. I throw in one Greater Quintessence of Fortitude (Flat Health) myself, as the 7 bars of health at level one if great for solo top.

With the recent release of the new masteries, I have had to redefine how I build Mordekaiser. The Improvements are substantial for tanks: More Gold, More Health, More Regen, More CC Reduction, and More Damage Reduction. Everything you could want for a tank has just been improved with these new masteries. What you might lack in Damage from putting so many points in Defense, you make up by being able to stay in the fight longer. And, after all, that's your job anyway.

Doran's Shield - It will keep you alive longer then anything else. Especially when soloing top, it will keep you laning longer. This with a regrowth pendant, and you never have to go back (aka you can go back at the optimal time, rather then being forced to go back while you turret gets destroyed.)

Sorcerer's Boots - Movement is key for harass and getting kills, as well as survival. Merc Treads may be a better choice depending on the opposing teams amount of CC.

Rylai's Crystal Scepter - Perhaps as important as boots, this item can let you escape, or slow their whole team in one attack. Gives you nice AP and Health too boot.

Force Of Nature - Completes all the Regen you will need, combined with the MR and Movement Speed make this item a must for Mordekaiser.

Sunfire Cape - This stacks amazingly with your "W" and the armor and health help a lot. This reminds me of Dr. Mundo, who chases enemies with his AoE fire ability on.

- At this point most of my games are already decided, but for those lengthy games here are some good picks -

Hextech Gunblade/WoA - Both help act as a "Second Shield" as they regen your health in team fights. Gunblade is more expensive, but has better stats and adds a Damage-slow as well.

Rabadon's Deathcap - I get this if I feel my team isn't doing enough damage, doubles your AP for a nice Damage boost.

Guardian Angel - A second life to keep going on. However, enemies may be even less inclined to attack you if they see the shield around you, which is bad when your job is to tank.

Not much to say here, I might throw a few points into creeping death sooner if I want some more survival.
Level up "E" as it can provide great harass and farm.

Ghost - Great for getting kills early game, escaping, chasing, and just getting were u need to be.

Ignite - Great combo with Ult to get some early kills, also great for late game damage as well.

Flash - Can be used, but with ghost you shouldn't need this.

Some other spells such as Heal, Exhaust, and Teleport can be considered, but each one has its pros and cons.

AoE - Area of Effect. This refers to abilities that hits multiple targets in a set area, however I use it to refer to any Multi-Target abilities.

Harass - Widdling down your enemies with short bursts of damage, followed by retreating to a safe range. Over time they will either die or be forced to leave.

CC - Crowd Control. Any effect that alters a champions ability to move/attack or react. Examples are: Taunts, Knock-ups, Slows, Rooting in Place, Forced movement (Such as Singed Fling or Alistar Charge) etc. Abilities such as Anivia's wall aren't really CC, though they have a similar effect.

Nerf - When the power of something is significantly diminished in a patch. If a champion is unbalanced, Riot may nerf them to more a reasonable level.

Patch - When Riot makes changes to game play, be it new champions, changing old champions, or Big Patches such as the Dominion Patch. These often occur on Tuesdays.

Some people still complain when I choose Morde, claiming he has no shield and is bad since the nerf. Immediately post-nerf I thought the same, however I have since learned this too be false.
In this build Morde has enough tankyness too not rely so much on his shield. That being said, he definitely benefits from his shield since you will be in the middle of 5 champions, with all your aoe building it up.

Mordekaiser is still quite strong and can be a great asset to any game.
Please comment below with any thoughts or ideas.