(Dragonskull Key isn't a spell.)

At the beginning of your end step, if you didn't cast any spells this turn, Dragonskull Key deals 1 damage to you.

Dragonskull Key is indestructible. (Destroy effects and lethal damage don't destroy it.)

: Add  to your mana pool. Dragonskull Key doesn't untap during your next untap step.