Glintstone Dragon Smarag

Flying, Haste
Whenever Glintstone Dragon Smarag attacks,
add X mana in any combination of colors,
where X is the total power of attacking creatures.
Spend this mana only to cast spells.
Until end of turn, you dont lose this mana as
steps and phases end.
"Instead of breathing fire, Smarag discharges
Glintstone-charged breath."