Merfolk Trickster
Oracle Text
Flash
When Merfolk Trickster enters the battlefield, tap target creature an opponent controls. It loses all abilities until end of turn.
Card Rulings
4/27/2018 Once you announce that you’re casting a spell or activating an ability, no player may take other actions until the spell or ability has been paid for. Notably, players can’t try to remove a permanent’s activated abilities to stop them from happening. Once activated, the ability on the stack will resolve even if the creature loses the ability.
4/27/2018 If the target creature has an ability that triggers when it becomes tapped, that ability triggers before it loses all abilities.
4/27/2018 If the target creature has power and toughness written as */* with an ability that defines its power and toughness, it’s 0/0 when it loses all abilities. If its power and toughness are written as */*+1, it’s 0/1, and so on.
The tap ability can buy a turn against a huge attacker (or knock out a big blocker) like a Wurmcoil Engine or Death's Shadow. The ability loss effect is generally less relevant as many common creatures rely on ETB effects that this can't stop, though it does halt an attacking Tarmogoyf or Signal Pest with ease.
It's a merfolk wizard, though. It works with Inalla in commander and someone is going to experiment with this thing in merfolk decks. I'm keeping an eye on this card.