Firebend is a keyword that will provide an amount of Red mana equal to the level of firebend a creature has
Once Fangorn, Tree Shepherd leaves the battlefield, you have until the end of the current step or phase to spend whatever green mana is in your mana pool before it too empties as normal
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of Thrill) 7, 5, 8: Collective Brutality (most flexible 2 cmc discard outlet in BRG) 6, 3, 4: Faithless Salvaging (slow, weak, only generates CA in late game) 5, 6, 5: Territorial Kavu (even slower because requires attack trigger) 4, 7, 7: Seasoned Pyromancer (both powerful and flexible, can generate bodies or CA) 3, 7, 8: Liliana of the Veil (powerful and flexible, threat + removal + discard) 2, 8, 8: Fable of the Mirror-Breaker Flip (slowest 3 cmc option, tons of grind power + flexibility) Additional notes: Bone Shards can be used to sacrifice an Ilharg or Emrakul, and if you sacrifice Ilharg it won't get exiled in order to reanimate it again next turn