Using Creatures
From Archon Arcana - The KeyForge Wiki
When the active player uses a creature, that player must exhaust the creature, and the player has the option to reap, fight, resolve the creature’s “Action:” ability, or resolve the creature’s “Omni:” ability. Any card effect that causes a creature to fight, reap, resolve its “Action:” ability, or to resolve its “Omni:” ability is causing that creature to be used.
—KeyForge Master Rulebook v17.3 March 2024