Ultra Beast Kartana

Wormhole — At the beginning of your upkeep,
you may exile Ultra Beast Kartana from your
hand. At the beginning of combat on your
turn, you may pay {1}{g}{g}. If you do, put Ultra
Beast Kartana onto the battlefield tapped and attacking. Sacrifice it at the end of combat.
Whenever Ultra Beast Kartana deals combat
damage to a player, add {g} for each creature that attacked this turn. You don't lose this mana as
steps and phases end.