Just a few suggestions:
Felidar Soverign - Win Condition
card:Conjurer's Closet - ETB effece usage and lifegain with Trostani
Nevermore - Depending on your playgroup, this card can win games for you if they don't have an answer. The only games I lose with my trostani deck are from Infinite combos or Commander / Poison Damage. This card will let you take out one persons commander for at least a tur or two. Better in 1v1 than multiplayer of course, but you can still use it to gain some political friends if someone looks like they are going to win and you can stop them with this.
Collective Blessing - 3 extra health on ETB with Trostani and turns mana dors into beaters.card:Cathars' Crusade can help with this as well.