Stormsplitter and Sorcerer Class on the battlefield.
You have another instant or sorcery card in hand with the mana to cast it.
Sorcerer Class is at least level 2.
({10} magic symbol) at most, depending on how many Stormsplitters and/or other creatures you control without summoning sickness available.
Steps
Cast the additional instant or sorcery by paying its mana cost.
Each Stormsplitter you control triggers, and Sorcerer Class's third ability triggers if it is level 3.
Resolve the Stormsplitter triggers, creating that many token copies of Stormsplitter.
Resolve the Sorcerer Class trigger, if applicable, dealing damage to any target equal to the number of instant and/or sorcery spells you've cast this turn.
Holding priority, activate any creature you control that does not have summoning sickness by tapping it, adding ({R} magic symbol) that can only be spent to cast an instant or sorcery spell, or to gain a Class level.
Repeat step 5 until you control no untapped creatures without summoning sickness, or until you have ({4} magic symbol) ({R} magic symbol) ({R} magic symbol) available, whichever comes first.
Cast Reiterate with buyback by paying ({4} magic symbol) ({R} magic symbol) ({R} magic symbol) , targeting the instant or sorcery cast in step 1.
Each Stormsplitter you control triggers, and Sorcerer Class's third ability triggers if it is level 3.
Resolve the Stormsplitter triggers, creating that many token copies of Stormsplitter.
Resolve the Sorcerer Class trigger, if applicable, dealing damage to any target equal to the number of instant and/or sorcery spells you've cast this turn.
Resolve Reiterate, copying the instant or sorcery, and returning Reiterate to your hand.
Resolve the copy of the instant or sorcery.
Repeat from step 5.
Results
Infinite LTB.
Infinite ETB.
Infinite damage.
Infinite storm count.
Infinite creature tokens with haste.
Infinite magecraft triggers.
Infinite copies of instant and sorcery spells on the stack.
Infinite blue mana that can only be spent to cast instant and/or sorcery spells.
Infinite red mana that can only be spent to cast instant and/or sorcery spells.