Defender When Barrier of Bones enters the battlefield, surveil 1. (Look at the top card of your library. You may put that card into your graveyard.)

Skeletons you control and other Zombies you control get +1/+1 and have deathtouch.

Skeletons, Vampires, and Zombies you control get +1/+1. At the beginning of your end step, if a creature died this turn, you may pay {1}. If you do, create a 1/1 black Skeleton creature token.

{B}: Regenerate Drudge Skeletons. (The next time this creature would be destroyed this turn, it isn't. Instead tap it, remove all damage from it, and remove it from combat.)

Other black creatures you control get +1/+1. {2}{B}, {T}: Another target black creature you control gains deathtouch until end of turn. (Any amount of damage it deals to a creature is enough to destroy it.)

{B}: Regenerate Restless Dead.

Flying When Skeletal Vampire enters the battlefield, create two 1/1 black Bat creature tokens with flying. {3}{B}{B}, Sacrifice a Bat: Create two 1/1 black Bat creature tokens with flying. Sacrifice a Bat: Regenerate Skeletal Vampire.

Whenever Underworld Sentinel attacks, exile target creature card from your graveyard. When Underworld Sentinel dies, put all cards exiled with it onto the battlefield.