Hello Summoners, I am Steven and I love playing supp with Alistar because I think that he is really op.

Summoner spells for support are good almost only flash and exhaust, because with flash u can initiate fight or have some run option.

Starting items
Starting item Ancient coin is really good for Alistar, because he is melee and he can´t play offensive early game so he will get better amount of gold from another gold items. And he gets enough mana to stay in lane till lvl. 9 without dying and with getting some assists if his adc is good.
Early game
Get Sightstone, because your adc really needs some vision in bushes and if he is smart he will harras enemy supp without getting any dmg. U must get early Greater Vision Totem, because u can have put only 1 vision ward and if u have this item u will never have to buy vision ward.
Mid game
If u get Aegis of legion and your adc Last whisper u must win every fight on lane, because your adc will have much more armor than enemy adc and u have smash and nockback and if they deal u some dmg just turn up your ulty and win fight.
U will need boots of mobility so u can use them to initiate fight faster and knockback enemy adc to your adc and then smash ground when u come back to that enemy adc.
Late game
because u are heavy tank and u get a lot of armor from your ulty u don´t need much of it so just buy Warmog and Randuins so you can toverdive enemy turret without getting much dmg.

Build 0-9-21 because of gold advantage in Utility. In defense take block to be better tank in early game, same as unyielding. Another things from defensive tree i see most important most hp and hp regeneration so i choose that 3.

Greater Seals is defensive tree and the best runes are Seal of armor. In Greater Marks i don´t really don´t know what to pick but best choice for me is combine attack dmg and magic penetration. In Greater Glyphs there is only good magic resist and because we play on lane against adc we just take half magic resist and half magic resist per lvl.

I have played him not much in ranked games, but i have 56% win rate with him. My average score is 0.9/game kills 4.8/game deaths and 14.1/game assists. So from my point of view i see him really good.