Alarm

Rite 1 (At the beginning of your turn, put a Rite counter on this spell. While this spell has less
than (1) Rite counters, it's effects are ignored)
{t}: Remove any spells assigned to this spell.
Then, you may assign a spell from your hand
to this spell.
{t}: When a creature enters the battlefield
under your opponent's control, you may cast a
copy of the assigned spell by paying it's cost.