Colliryao, the Marsh Bringer

When Colliryao enters the battlefield, put a Marsh
counter on target land. You may pay {1}{b}{g}{u}. If you
don't, sacrifice Colliryao at the beginning of the next end
step.

At the beginning of your upkeep, choose a counter
on a permanent. Put a counter of that kind on target
permanent if it doesn't have a counter of that kind
on it.

Whenever a player taps a land with a Marsh counter on it you may add {b}, {g}, or {u} to your mana pool.