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

: Add  or to your mana pool.

Put Tidal Ampitheater on top of your library: Add  to your mana pool.

: Tidal Ampitheater becomes a 2/1 blue and red Cephalid creature until end of turn. It's still a land.