Spellbinding Soprano's encore ability by paying ({3} magic symbol) ({R} magic symbol) and exiling it from your graveyard, creating a token copy of it with haste for each opponent you have.
Declare each
Spellbinding Soprano token as an attacker.
Each
Spellbinding Soprano token triggers, causing instant and sorcery spells you cast this turn to cost ({1} magic symbol) less to cast for each
Spellbinding Soprano token.
Cast
Seething Anger with buyback by paying ({R} magic symbol) .
Birgi triggers, adding ({R} magic symbol) .
Resolve
Seething Anger, giving target creature +3/+0 until end of turn and returning
Seething Anger to your hand.
Repeat from step 4.
Results
Infinite magecraft triggers.
Infinite storm count.
Infinite power for creatures you control until end of turn.