Shell Sanctuary

Shell Chamber (At the beginning of your upkeep,
you may exile a creature you control. If you do,
put a shell counter on Shell Sanctuary.)
{t}:Add one mana of any color.
{t}:Remove three shell counters from Shell Sanctuary: Return a creature card exiled with Shell Sanctuary
to the battlefield under its owner's control.

"A haven for the weary, where protection is as
enduring as the shell."