Aven Mindcensor

Flash
Flying
If an opponent would search a library, that player searches the top four cards of that library instead.

Battlefield Scavenger

You may exert Battlefield Scavenger as it attacks. (It won't untap during your next untap step.)
Whenever you exert a creature, you may discard a card. If you do, draw a card.

Combat Celebrant

If Combat Celebrant hasn't been exerted this turn, you may exert it as it attacks. When you do, untap all other creatures you control and after this phase, there is an additional combat phase. (An exerted creature won't untap during your next untap step.)

Ahn-Crop Crasher

Haste (This creature can attack and {T} as soon as it comes under your control.)
You may exert Ahn-Crop Crasher as it attacks. When you do, target creature can't block this turn. (An exerted creature won't untap during your next untap step.)

Resolute Survivors

You may exert Resolute Survivors as it attacks. (It won't untap during your next untap step.)
Whenever you exert a creature, Resolute Survivors deals 1 damage to each opponent and you gain 1 life.

Ahn-Crop Champion

You may exert Ahn-Crop Champion as it attacks. When you do, untap all other creatures you control. (An exerted creature won't untap during your next untap step.)

Glory-Bound Initiate

You may exert Glory-Bound Initiate as it attacks. When you do, it gets +1/+3 and gains lifelink until end of turn. (An exerted creature won't untap during your next untap step.)