Duucxejial, "Golden Tone"

Dragon spells you cast cost {r/g}{r/w} less to cast.
Mei'ensou — {r}{g}{w}, {t}: Duucxejial, "Golden
Tone" deals 2 damage to each attacking or
blocking creature your opponents control. Until
end of turn, those creature lose indestructible
and can't be regenerated. If those creatures
would leave the battlefield this turn, put them
on the bottom of their owners' libraries instead.