Arcanivore Frostform

When Arcanivore Frostform enters the
battlefield, you may tap up to X target creatures.
Those creatures gain a Revivifaction counter.
{c}{c}{w/u}: Reviviform valid target Host:
- When Host creature attacks, its controller may
tap a number of creatures defending player
controls equal to the number of Revivifaction
counters on Host creature.