Not Updated For Current Season
The masteries shown here are not yet updated for the current season, the guide author needs to set up the new masteries. As such, they will be different than the masteries you see in-game.
this build is for an alistar tank. you get a good amount of magic resist, as well as good health, and considerable armor. obviously, as a tank character you have to adjust depending on the situations, but this is a very good build for going against a melee heavy team, and the magic resist helps as well. you get two auras, so you support a little that way, and you can really take the damage they can deal. heal and clarity supplement the idea of being good support, and also for clarity because you run out of mana very quickly. the heal is nice for lane presence, and for a surprise in a team fight perhaps? :)
GL and HF playing allistar!