Hostile Negotiations

Exile the top three cards of your library in a face-down pile, then exile the top three cards of your library in another face-down pile. Look at the cards in each pile, then turn a pile of your choice face up. An opponent chooses one of those piles. Put that pile into your hand and the other into your graveyard. You lose 3 life.

Cathar Commando

Flash (You may cast this spell any time you could cast an instant.)
{1}, Sacrifice this creature: Destroy target artifact or enchantment.

Spark Double

You may have Spark Double enter as a copy of a creature or planeswalker you control, except it enters with an additional +1/+1 counter on it if it's a creature, it enters with an additional loyalty counter on it if it's a planeswalker, and it isn't legendary.

Doomed Necromancer

{B}, {T}, Sacrifice Doomed Necromancer: Return target creature card from your graveyard to the battlefield.

Vile Entomber

Deathtouch (Any amount of damage this deals to a creature is enough to destroy it.)
When this creature enters, search your library for a card, put that card into your graveyard, then shuffle.

Frantic Search

Draw two cards, then discard two cards. Untap up to three lands.

Sister Hospitaller

Medicus Ministorum — When Sister Hospitaller enters, return target creature card from your graveyard to the battlefield. You gain life equal to its mana value.

Panharmonicon

If an artifact or creature entering causes a triggered ability of a permanent you control to trigger, that ability triggers an additional time.

Preston, the Vanisher

Whenever another nontoken creature you control enters, if it wasn't cast, create a token that's a copy of that creature, except it's a 0/1 white Illusion.
{1}{W}, Sacrifice five Illusions: Exile target nonland permanent.