You control at least three creatures without summoning sickness.
Steps
Activate three creatures you control by tapping them, adding ({2} magic symbol) ({U} magic symbol) that can only be spent to cast instant and/or sorcery spells, or to gain a Class level.
Cast
Mystic Speculation with buyback by paying ({2} magic symbol) ({U} magic symbol) , triggering
Jeskai Ascendancy's first and second abilities and
Sorcerer Class's third ability if it is level three.
Resolve the
Sorcerer Class trigger, if applicable, causing
Mystic Speculation to deal an amount of damage to each opponent equal to the number of instants and sorceries you've cast this turn.
Resolve the first
Jeskai Ascendancy trigger, giving creatures you control +1/+1 until end of turn and untapping them.
Resolve the second
Jeskai Ascendancy trigger, allowing you to loot.
Resolve
Mystic Speculation, causing you to scry 3 and return
Mystic Speculation to your hand.
Repeat.
If you control four or more creatures without summoning sickness, this combo nets near-infinite mana.
Results
Infinite draw triggers.
Infinite looting.
Infinite self-discard triggers.
Near-infinite blue mana that can only be spent to cast instant and/or sorcery spells.
Near-infinite damage.
Near-infinite power and toughness for creatures you control until end of turn.
Near-infinite magecraft triggers.
Near-infinite red mana that can only be spent to cast instant and/or sorcery spells.
Near-infinite storm count.
Near-infinite untap of creatures you control.
Near-infinite mana creatures you control can produce.