When Treeguard Duo enters, until end of turn, target creature you control gains vigilance and gets +X/+X, where X is the number of creatures you control.
"You shall not pass me," croaked the frog. "Nor me," growled the rabbit.
The value of X is determined only as Treeguard Duo’s triggered ability resolves, potentially including Treeguard Duo itself. It won’t change later in the turn if the number of creatures you control changes.
Random a card of Magic: The Gathering (MTG), but you can also roll the D20 dice, random a Planeswalker, have fun with the random rules and more.