Imp's Mischief

Change the target of target spell with a single target. You lose life equal to that spell's mana value.

Caustic Crawler

Landfall — Whenever a land you control enters, you may have target creature get -1/-1 until end of turn.

Muck Drubb

Flash
When Muck Drubb enters, change the target of target spell that targets only a single creature to Muck Drubb.
Madness {2}{B} (If you discard this card, discard it into exile. When you do, cast it for its madness cost or put it into your graveyard.)

Bloodghast

Bloodghast can't block.
Bloodghast has haste as long as an opponent has 10 or less life.
Landfall — Whenever a land you control enters, you may return Bloodghast from your graveyard to the battlefield.

Withering Boon

As an additional cost to cast this spell, pay 3 life.
Counter target creature spell.

Dreadwurm

Landfall — Whenever a land you control enters, Dreadwurm gains indestructible until end of turn. (Damage and effects that say "destroy" don't destroy it.)