Billingr, the Far-Wanderer

Cumulative upkeep—Add {g} (At the beginning of
your upkeep, if this permanent is on the battlefield, put
an age counter on this permanent. Then you may pay
its upkeep cost for each age counter on it. If you don't, sacrifice it.)
Mana doesn't empty from your mana pool as
steps and phases end.
Hexproof from black and from red