Card Rulings

Once a player announces that they’re casting a spell or activating an ability, no player may take other actions until the spell or ability has been paid for. Notably, other players can’t try to tap that player’s permanents to stop them from paying   or to stop them from producing enough mana.

You can tap any untapped creature you control to activate Opposition’s ability, even one you haven’t controlled continuously since the beginning of your most recent turn.