Shadows over Innistrad Remastered

Spell Queller | Creature | Spirit | Flash Flying When Spell Queller enters the battlefield, exile target spell with mana value 4 or less. When Spell Queller leaves the battlefield, the exiled card's owner may cast that card without paying its mana cost. | Adam Paquette

Prized Amalgam | Creature | Zombie | Whenever a creature enters the battlefield, if it entered from your graveyard or you cast it from your graveyard, return Prized Amalgam from your graveyard to the battlefield tapped at the beginning of the next end step. | Karl Kopinski

Olivia, Mobilized for War | Legendary Creature | Vampire Knight | Flying Whenever another creature enters the battlefield under your control, you may discard a card. If you do, put a +1/+1 counter on that creature, it gains haste until end of turn, and it becomes a Vampire in addition to its other types. | Eric Deschamps

Mournwillow | Creature | Plant Skeleton | Haste Delirium — When Mournwillow enters the battlefield, if there are four or more card types among cards in your graveyard, creatures with power 2 or less can't block this turn. | Jeff Simpson