Impact Tremors

Whenever a creature you control enters, this enchantment deals 1 damage to each opponent.

Soul's Attendant

Whenever another creature enters, you may gain 1 life.

Renegade Doppelganger

Whenever another creature you control enters, you may have Renegade Doppelganger become a copy of that creature until end of turn. (If it does, it loses this ability for the rest of the turn.)

Norin the Wary

When a player casts a spell or a creature attacks, exile Norin the Wary. Return it to the battlefield under its owner's control at the beginning of the next end step.

Phantasmal Image

You may have Phantasmal Image enter as a copy of any creature on the battlefield, except it's an Illusion in addition to its other types and it has "When this creature becomes the target of a spell or ability, sacrifice it."

Ponder

Look at the top three cards of your library, then put them back in any order. You may shuffle.
Draw a card.

Soul Warden

Whenever another creature enters, you gain 1 life.

Scout's Warning

The next creature card you play this turn can be played as though it had flash.
Draw a card.

Brainstorm

Draw three cards, then put two cards from your hand on top of your library in any order.