Enchanted creature doesn't untap during its controller's untap step.
Entangling Vines can enchant only a creature that’s tapped. If at any time the enchanted creature is untapped, Entangling Vines is put into its owner’s graveyard as a state-based action.
If Entangling Vines is cast as a spell, it can target only a tapped creature. If the creature has become untapped by the time Entangling Vines would resolve, it’s countered and put into its owner’s graveyard from the stack.
