Leviathan, The Final Wave

Haste, Indestructible, Menace
At the beginning of your combat step, you may
have this card exile target land until Leviathan
leaves the battlefield. If you do, that permanent's
controller gains a 'Wave' artifact token with:
"{t}: add {u} to your mana pool."
Leviathan, the Final Wave gets +1/+0 for each
'Wave' token on the battlefield.