Stonecloaker

Flash
Flying
When this creature enters, return a creature you control to its owner's hand.
When this creature enters, exile target card from a graveyard.

Whitemane Lion

Flash
When this creature enters, return a creature you control to its owner's hand.

Stormfront Riders

Flying
When this creature enters, return two creatures you control to their owner's hand.
Whenever this creature or another creature is returned to your hand from the battlefield, create a 1/1 white Soldier creature token.

Dust Elemental

Flash (You may cast this spell any time you could cast an instant.)
Flying; fear (This creature can't be blocked except by artifact creatures and/or black creatures.)
When this creature enters, return three creatures you control to their owner's hand.

Ephara, God of the Polis

Indestructible
As long as your devotion to white and blue is less than seven, Ephara isn't a creature.
At the beginning of each upkeep, if you had another creature enter the battlefield under your control last turn, draw a card.

Saltskitter

Whenever another creature enters, exile this creature. Return this creature to the battlefield under its owner's control at the beginning of the next end step.