This build guide for Alistar is for support. Alistar is a tanky support champion. With multiple crowd control effects, heals, and toughness Alistar can be a valuable addition to any team.

Pros

-Good roaming
-Strong late game (AoE cc on short cooldown)
-One of the best peelers
-Good Towerdiver

Cons

W + Q Combos are a vital part of playing him and can be messed up easily which leaves you high and dry.
High skill cap.
Doesn’t really win lane versus anyone
Doesn’t have a burst lvl 6.

There are two different ways to successfully play Alistar as a support champion: aggressively and passively.

In an aggressive lane, you will want to pair Alistar with a strong AD carry who can easily burst and all in the enemy laners.
In such a lane, you will need to capitalize on enemy mistakes. Most importantly, make sure that the AD carry is able to follow up on anything you do. Level 2 Alistar has the most potential for a kill, whether it be a Flash+Pulverize (Q)+Headbutt (W), or a Headbutt (W) into a wall then Pulverize (Q). Do take note of the minion wave before engaging. Make sure to have as little ranged enemy minions as possible so that you will not receive so much damage from minions.

Against a non-sustain lane, engaging to do damage will allow you to zone your opponents, forcing them to base and lose vital cs and exp, or setting up for easy diives with your jungler

Against a lane with sustain, you will need to burn their summoners and/or kill them in order to make the all in worth while. Otherwise, they will outsustain and eventually beat you.

In a passive lane, your goal is to simply babysit and prioritize farming. Such a lane relies on a stronger late game (Kog’Maw/Ashe/Vayne) or to protect the laner against super aggressive supports (Leona/Taric) while being relavant in skirmishes as well.
This lane still has kill potential, but will only be able to win the lane in a 2v2 if they have an item or level advantage. You’ll need to make sure to give the carry in your lane the minion kills they’ll need to do their builds. You want to give your carry the best possible chance to farm as much gold as possible, as your team will rely on their damage mid and late game.

Using Pulverize immediately after a successful Headbutt will apply the stun from Pulverize. Instead of being pushed back, the target will be knocked up and stay in place. This can be useful in some chase situations (make sure you succeed or you will knock them further away), or finishing off a weakened opponent on the run. This combo is risky, leaves you useless while both abilities are on cooldown, and is extremely costly if missed. However, it is considered a staple move of Alistar and used very often in both competitive and casual play.

Flash Pulverize into Headbutt

Heabutting people into walls gives you more CC time so you can then pulverize them later.

On Alistar you should play defensively, as a carry peeler, focus on farming under turret and wait for the jungler to come. More often than not you’ll grab a kill due to your immense CC

Alistar has two possible roles in a teamfight - initiate or peel

Initiate:
An initiator works as a sponge for damage and crowd control spells. In Alistar's case, this also means the ability to initiate engagements with the enemy team. You will likely be using both Headbutt (W) and Pulverize (Q) on the enemy back lines, allowing for your team to follow up. However, as a reminder, Alistar will not be able to effectively tank damage in a lengthened fight due to his ultimate providing most of his tankiness. If your team can’t kill targets quickly, your team will need another tank or bruiser to absorb damage after Alistar’s ultimate expires. Furthermore, your carries will require peeling from your other teammates if support Alistar has to be the main initiate.
Peeling:
In most situations, Alistar should act as a peel for his carries, as his CCs are not affected by Tenacity or Cleanse. You should use Q(Pulverize) if the enemy bruiser is not so fed and can be killed by your carries. For extremely beefy and threatening tanks, always use W(Headbutt) to knock him away ASAP. If he closes the gap again, use Pulverize and Exhaust to disable them further.
You also want to be healing as many targets as possible on your team, but protecting your fed carries should be your first priority.

Headbutt and Pulverize Combo
One of the reasons why Alistar is one of the highest skill cap Support champions is because of the Headbutt-Pulverize combo. It is difficult to pull off consistently and requires practice to get right. As you can tell in the video below, even Hotshotgg has difficulty with this during games. The key is to not hit the keys too quickly together or too late apart. There is a magic timing that will allow you to pull it off that is difficult to describe or write about. You simply just need to practice it, over and over and over until it feels natural. The timing gets tricky as the distance varies, so practice makes perfect!

Alistar is one of most aggressive support champions, perhaps as aggressive as Leona. Because of this, you can go for a ‘kill lane’ in the duo bot lane. This strategy can pay off if you can get kills, but if not; it might backfire.

Alistar has a strong level one fight, which enables your team to invade the enemy jungle. A strong level 1 engagement might pay off for your team and snowball you into a victory.

Alistar has a very strong initiation. If he Flash Pulverizes into the enemy team during mid or late game, it can be followed up by your allies with additional AOE damage or Crowd Control. Alistar can immediate use his ultimate to ‘cleanse’ out of any crowd control from the enemy team; allowing him to then back out, wait for cooldowns and then continue to cc on the enemy carries.

Alistar has good sustain in lane for the duo laning

phase. There are four main supports that have a heal, Sona, Soraka, Taric and Alistar. Alistar’s heal, while not as powerful, has a decent cooldown and can assist in making sure your lane has enough sustain to continue farming.

Alistar can absolutely punish anyone out of position. By having two built-in abilities that cause a stun and knockup; it can immobilze the enemy champion long enough to be bursted down before the enemy team comes to assist them.

He is one of the more difficult support champions to play. There are critical times in the game that will REQUIRE you to hit your Headbutt, Stun combination. If you miss it, you might have missed the perfect opportunity to catch someone off guard on the enemy team.

Work on learning the W-->Q instant combo to catch someone running away. It’s quite difficult to get the timing down, but once you do, it can become a great asset to your Alistar arsenal.

A common mistake many Alistar players make is waiting until they are already very low on health to use Unbreakable Will (R). You want to use your ultimate when you’re high on health as you initiate a fight to increase your chances of survival.