Snaremaster Sprite
Creature — Faerie Wizard
Flying
When this creature enters, you may pay 
. When you do, tap target creature an opponent controls and put a stun counter on it. (If a permanent with a stun counter would become untapped, remove one from it instead.)
Christina Kraus
Wilds of Eldraine (WOE)
• #68Rulings
You may target a creature that is already tapped with the reflexive triggered ability. If the target creature is already tapped as the ability resolves, you will still put a stun counter on it.
(wotc • 2023-09-01)
You don't choose a target for Snaremaster Sprite's ability at the time it triggers. Rather, a second "reflexive" ability triggers when you pay {2} this way. You choose a target for that ability as it goes on the stack. Each player may respond to this triggered ability as normal.
(wotc • 2023-09-01)
Rulings
You may target a creature that is already tapped with the reflexive triggered ability. If the target creature is already tapped as the ability resolves, you will still put a stun counter on it.
(wotc • 2023-09-01)
You don't choose a target for Snaremaster Sprite's ability at the time it triggers. Rather, a second "reflexive" ability triggers when you pay {2} this way. You choose a target for that ability as it goes on the stack. Each player may respond to this triggered ability as normal.
(wotc • 2023-09-01)