3.17.2014 : Edited the "Early Game" Chapter.
3.17.2014 : Added "ITEMS" Chapter. Fixed Mastery Page.

The truth is, there can be many changes into the build and it can still work. For example, Talisman of Ascension can be rushed first than the Deathfire Grasp. It will give you the small boost in movement speed to easily catch opponents in bottom lane.

However, Deathfire Grasp should be bought before Mid-Game (~20 minutes). Usually after my starting items, I get my mobility boots, pots, and wards. Then I save up for my Needlessly Large Rod, only for the fact that the build makes Alistar really weak early anyway, so might as well just save gold.

Sometimes I buy a Sheen before my Deathfire Grasp. This is usually if my ADC has enough damage, then OCCASIONALLY I buy myself a lichbane first. But, keeping a Sheen is usually sufficient for early game. However, make sure you auto in between your skills if you buy yourself one!

After the first three or four items, the last two items do not really matter. I sometimes go Randuin's Omens if I see that they're AD Heavy, and they're extremely hard to catch. Omen's would definitely help slow them, and slow them even more if they auto attack you.

Rabadon's Deathcap can also be bought if you are doing so well with your team.

Okay. At first, you may be going like "WTF!?@#?!@#" Well. I understand. These runes are a bit weird. But your goal as an AP Alistar is to be SCARY.

Greater Quintessence of Movement Speed x9 : Gives you the movement speed in order to play aggressive and pull off your combo easier.

Greater Mark of Hybrid Penetration x9 : Again, like the Devastating Strikes , it gives armor and magic pen. With these hybrid marks, you can deal A LOT more damage without having too much AP in the beginning.

Greater Seal of Armor x9 : Armor is just necessary for all bottom lanes.

Greater Glyph of Mana Regeneration x4 : Mana regeneration is also necessary for someone like Alistar. He constantly heals, and needs to constantly put those combos in. If he runs out of mana, his scary presence in lane drops down to ZERO. Meaning, automatic death unless you go back to recall and heal your mana.

Greater Glyph of Magic Resist x5 : Magic Resist is also needed.

These runes give a BIT of tankiness, as well as strength. You will need both in order to emerge as the better support near late game.

Your early game is weak as Alistar, especially with this build set up. Nevertheless, you're still an Alistar, and can peel and play aggressively well - two things not a lot of supports can do at the same time. However, when he goes in, it is usually an all-in.

As I said before, his early game is very weak. Regardless, he can still play aggressively. He's weak early game because his damage is poop compared to Lulu or Sona. He still deals a fair amount of damage with his combo and autos, but not worth it for the mana cost.

He's good at setting up ganks. IF they decide to go all-in, or let's say a Thresh pulled into you, you can pulverize, knock him back for the jungler to come and take the kill. Or, he can Headbutt someone into the wall, and then Pulverize.
(Make sure the bush is warded if you headbutt them into a bush.)

And one last time, I cannot stress enough on how WEAK WEAK WEAK WEAAAAAK his early game is. So don't go yolo YET.

Once you get your Deathfire Grasp, nothing will change except for the fact that you're bursty. As you get more items to make you stronger, the tanks will get more items to make themselves tankier. MEANING, you will always deal the same amount of damage to them, unless they get a lot more fed. However, carries usually build only one or SOMETIMES two survivability items. They won't be getting too tanky for you to rip them apart.

As Alistar, you should usually stick with your ADC, or atleast someone who can burst someone down quickly. Your combo should be DFG, W, Q, Auto, Move, Auto, Heal, Move, Auto, etc. You should ALWAYS put in some auto attacks.

But overall, play aggressively always as AP Alistar. You're not a peeling machine. Although you have abilities that can peel well, most of the time you should focus on one-shotting carries. Although a tank Alistar may do better in a teamfight overall that drags on, if played well, an AP Alistar can do a lot more. One-shotting their ADC to make a fight 5v4 can be one thing. OR even comboing into their team to deal a lot of damage.

Shortly, there will be a video showing you an example of a teamfight when playing this build.

Normally, you play yourself almost like a carry, but at the same time, a support. Your job is to carry or help your team as much as possible in a team fight. MEANING, if peeling is necessary, then PEEL. Imagine yourself as an Orianna, - you jump into the middle of their team and CC ALL OF THEM - except you're a melee, and not a robot.

In a team fight, if you find any opportunities to strike a squishy carry, then do it. You have a Deathfire Grasp to amplify all your damage abilities, one of them being a knockup. This can literally turn around a whole teamfight, because if you are strong enough, you forced the carry to burn one or two of their Summoners, or run away to play safe. Either way, you've done **** tons of damage to their carry.
After you combo, you can continue to fight, or retreat for your next combo, while healing your team. The good thing is, you have an ultimate that makes you slightly tankier. This is what makes an AP Alistar different than any other supports/carries. He removes all CC, while gaining some tankiness. This can mean that he can last longer than any other carries in a teamfight. NOW, if they focus you, that's stupid of them. They're wasting time to kill a support. But if you don't die, you'll have your next combo up! Yeah, AP Alistar is THAT ******ed.

While being able to instagib squishy champions, again, you're one of the best initiators in the game. You have mobility boots, Talisman at times, and if you have any other movement speed boosts, that's even better. If you outrun the enemies by far in a chase, you don't have to exactly combo them. You can flash ahead of them and Headbutt them back.