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

When Debris Tubes enters the battlefield, put a land you control on the bottom of its owner's library.

: Add  to your mana pool.

: Debris Tubes becomes a 2/1 blue and black Crab Merfolk creature until end of turn. It's still a land.