Wall of Frost

Defender
Whenever Wall of Frost blocks a creature, that creature doesn't untap during its controller's next untap step.

Barrier of Bones

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.)

Thoughtbound Phantasm

Defender
Whenever you surveil, put a +1/+1 counter on Thoughtbound Phantasm.
As long as Thoughtbound Phantasm has three or more +1/+1 counters on it, it can attack as though it didn't have defender.

Blight Pile

Defender
{2}{B}, {T}: Each opponent loses X life, where X is the number of creatures with defender you control.