Can you activate Sett's (champion card) ability on the opponent's turn after he gets blitz hooked?

Ruling: No, you cannot activate Sett's ability on the opponent's turn. If an ability doesn't say Action or Reaction, you can't use it as if it were an action or reaction.

Nuances:

• This applies to Sett the champion card that spends buffs, not Sett Legend
• Sett Legend's ability is a replacement effect that applies at any moment a buffed unit would die, which works differently