Aetherling

{U}: Exile Aetherling. Return it to the battlefield under its owner's control at the beginning of the next end step.
{U}: Aetherling can't be blocked this turn.
{1}: Aetherling gets +1/-1 until end of turn.
{1}: Aetherling gets -1/+1 until end of turn.

Pioneer Masters

Dragon's Maze

{U}: Exile Ætherling. Return it to the battlefield under its owner's control at the beginning of the next end step.
{U}: Ætherling is unblockable this turn.
{1}: Ætherling gets +1/-1 until end of turn.
{1}: Ætherling gets -1/+1 until end of turn.

Aetherling’s first ability will return it to the battlefield only if that ability also exiled it. If Aetherling left the battlefield in response to that ability, it won’t return, even if it was exiled by another spell or ability.

Aetherling’s last ability can be activated even if its power is 0 or less. If a creature would assign 0 or less damage in combat, it doesn’t assign combat damage at all.