Abzan Prison is a control deck so named because it uses Prison Realm style effects to control the game.
It is a classic "kill your stuff deck", so to speak -- most of the deck revolves around removal of some sort, whether it be O-Ring effects, board wipes, or single target kill/exile spells. Its primary win conditions are Dawn of Hope and Kaya, Orzhov Usurper. Kaya and the other effects can exile enough cards that her ultimate will deal lethal damage. When winning with Dawn, a win can come from Dawn itself by grinding out a win with the 1/1 Soldier tokens swinging every turn and removing anything that can stop them, or it can come from Vraska, Golgari Queen using her ultimate to give them losstouch or from Wilderness Reclamation speeding up the clock on how fast I can make soldiers.
Ajani, the Greathearted is another way to accelerate a win once control has been established by buffing the tokens, and it also serves as a lifegain engine while trying to establish control. The Birth of Meletis does several things I like -- it draws a land from my deck so I don't miss land drops and don't draw dry in the lategame, it makes a 0/4 wall that I can use to stay alive, and it heals me to help me stay alive while establishing control.
While Calix prefers to stack exiles on an O-ring enchantment, he can use Dawn of Hope, Wilderness Reclamation, or even Omen of the Sun or The Birth of Meletis as an O-ring in a pinch if he has to urgently remove a threat. Even a one turn removal of a God can be enough for me to hit my board sweeper and remove the devotion. He also draws Dawn of Hope, Wilderness Rec, BoM, and O-ring effects with his +1, and gets any back that the opponent managed to destroy if I ult him.
Kaheera doesn't do much as a companion, but I didn't have to change anything to run it, so why not? It's just a free 3/2 with Vigilance that can apply some pressure and serve as a blocker.
