Flash (You may cast this spell any time you could cast an instant.)
When Great Oak Guardian enters the battlefield, creatures target player controls get +2/+2 until end of turn. Untap them.
Great Oak Guardian’s last ability targets only the player, not any creatures. Creatures with shroud that player controls will be affected, for example.
Any creatures controlled by the player that are already untapped will just get +2/+2 until end of turn.