Skorath Unchained

Flying, Menace
Whenever Skorath Unchained attacks, roll a D12.
Add X mana in any combination of {r} or {g},
where X is the roll's result.
{r}{r}{r}{r}{r}{g}{g}{g}{g}{g}: Untap all creatures you control. After this phase, there is an additional
combat phase. Activate this ability only on your
turn and only once each turn.