As Mid Alistar, your main job is to dominate your lane, and roam. Say Top lane is getting shit on, well it's your job to roam and help him out. Let your jungler sit back and farm. He needs CS too. ALSO if you're behind, roaming is a great way to catch up. Get 6 assists from roaming TOP/BOT is the equivalent of getting 3 kills. That should help you greatly. Gets your top and ADC fed, and you end up with enough gold to get back in it.
Items and Explanations (not build order):
I go with the boots of mobility simply because it gives you more roam and chase potential. Plus, without boots of mobility, it's a necessity to bring ghost on mid alistar. Boots of mobility cancel out the ghost and allow you to exchange it for another summoner spell (ignite, clarity, tp, etc).
Twin shadows is one of the main items that allows you to survive, score in lane, and easily CC opponents early on through roam. It's also the cheapest item that you will build.
- It provides you with enough damage (40 AP + 15-20 starting AP from runes) to outdamage your enemy early on in lane into the mid game, in which you complete more items.
- It provides you with enough Magic Resist (40 MR + 12-15 starting MR from runes) to out-sustain your opponent in fights.
- It provides you with +6% move speed stacked onto the possible boots of mobility. It also supplies an active which summons ghosts that give sight and slow by 40% for a short duration. Both of these come in handy when:
A. chasing an opponent, who just so happens to have those easy mode escapes :)
B. being chased by opposing ganks that you may not have caught.
Rod of ages is in a way a catalyst for your build. It will assist you most during the late early game into mid game.
- Alistar is a very mana heavy champion. Alistar is also a very tanky champion. Given that he's naturally tanky in fights with his ultimate, it's great to have some defensive stats on the side.
- Also the Ability Power supplied increases Ali's Self heal Active (E) as well as his damage abilities.
- Rod of ages is also good because it gives you and your jungler a bit of a cushion. With the mana that is obtained through rod of ages, if you play smart, you may be able to sacrifice all future blue buffs past the first 2-3. This allows your jungler to take an additional buff and gain more gold, XP, and modify his jungle rotations.
Lich Bane is a strong side item because it supplies additional move speed, total mana, and Ability Power.
- Additional movement speed supplied by the Lich bane allows for stronger chase, engage, and disengage.
- Again this adds even more of a cushion between you and your jungler in a sense. The total mana allows you to pass the blue buffs onto either your jungler or another carry at this point in the game.
- The Passive Proc on the Lich Bane (after spell cast, next basic attack deals bonus magic damage equal to 50 + 75% of your Ability Power) is great going along with your combo. Alistar is a mid laner that relies heavily upon autoattacks in engages. This has a 2 second cooldown which is more than enough time for you proc it around 2 times during engages.
Sunfire cape is a strong late game item because of it's passive assistance during engages, but also because of the heal and armor stats. Sunfire is the go-to fifth item if you're ahead and the enemy team currently has any fed ad champions, this is a must have.
- 450 Health increases your tankiness stacked upon your ultimate and the stats gained from Rod of Ages.
- 45 Armor gives you the strength to make it to the back line, believe it or not. This is always not the case. During teamfights, if you have a support like Thresh, janna, Leona that has easy peel and can keep anyone and everyone off of your carries, then by God this is your opportunity. You have enough tankiness to jump through the enemy front line and get some good damage off meanwhile interrupting a possible ultimate by the enemy carry.
- A passive that deals 40 magic damage per seconds to nearby enemies is never a bad thing. Chances are the enemy carry is going to have no tankiness and is going to rely on peel to save their life. Passive sunfire damage supplies you with more than your base combo damage and allows for a nice extra bit of damage.
Ah yes! Say that enemy Rumble is 27-4 and your 2-23 teemo ragequit. You can still compete and not even replace that ragequitting boyscout. Just build one of these Spirit Visage Thingys. If the enemy AP is fed as all hell, then skip the sunfire cape. Spirit Visage provides you with more tankiness to dodge those abilities in teamfights.
- +50 Magic Resist is always good especially for tanking the front line aoe abilities combo'd with your ultimate.
- +200 hp just adds to your tankiness and awesomeness. need i say more?
- +20% Cooldown Reduction is great on Alistar. His cooldowns are so terribly long. This is the main reason why he relies so much on his autoattacks for a very large chunk of his damage.
- The Passive +20% of regen all around is also great stacked onto your E self heal.
- This is a lot more situational than Sunfire cape. because of the next item in this list that also supplies damage and Magic Resist.
Generally this is what takes the place of the Spirit Visage. It supplies enough magic resist for you to be tanky enough. Like previously stated, spirit visage is more situational, and generally relies upon the enemy AP being SUPER fed.
- Provides enough Magic Resist to combo with armor and HP from sunfire and other items.
- Supplies you with a wee bit of extra damage that just strengthens your combo in teamfights, while making you even more incredibly tanky combo'd with your ultimate.
- The aura passive that reduces enemy Magic Resist by 20 combos so well with you. Then again, how can making the enemy feel more of your damage on their health bars not combo well with anyone.
When you're behind
When you're behind you still rush a Twin Shadows. When you're behind as Mid Alistar, you roam and build as if you're supporting. This is stressed more in the other chapters.
After that, however, you want to rush a Will of the Ancients. When you're behind as alistar, the last thing you want to do is try and build so much freaking damage like you would if you were ahead. If you're behind, you want to end up building a little bit of damage, but majority tank and tanky aura items.
Which brings me to my next item:
Shurelya's is a good item on any support. Simply put, any item that builds out of a kindlegem is a good item on a support. This again just brings so much to the table. The active AOE speed boost, health, and all around regen just make it. Also it's good because it builds out of a philo which supplies extra gold per 10 when you're behind.
Basically if you're behind as Alistar mid, you must build almost exactly like you would as a support alistar. You want to be able to CC the enemy and help your teammates get kills as much as possible.