Cheapest priced copy (Dominaria): $0.49 at Card Kingdom, near mint, their price list as of .
Merfolk Trickster 
Creature — Merfolk Wizard · 2/2 · Uncommon · Dominaria · #56
Flash
When this creature enters, tap target creature an opponent controls. It loses all abilities until end of turn.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
2 printings · $0.49 to $4.99 at Card Kingdom
3 rulings from Wizards of the Coast
- 27 April 2018If 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.
- 27 April 2018Once 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.
- 27 April 2018If the target creature has an ability that triggers when it becomes tapped, that ability triggers before it loses all abilities.