Creatures you control can tap to produce at least ({2} magic symbol) .
({2} magic symbol) ({R} magic symbol) ({R} magic symbol) at least available.
Steps
Cast Great Train Heist by paying at least ({2} magic symbol) ({R} magic symbol) ({R} magic symbol) , choosing its first mode and optionally its second and/or third modes.
Kitsa's prowess ability triggers, giving it +1/+1 until end of turn.
Holding priority, activate any number of creatures by tapping them, adding at least ({2} magic symbol) .
Activate Kitsa's second ability by paying ({2} magic symbol) and tapping it, copying Great Train Heist.
Resolve the copy of Great Train Heist, untapping all creatures you control and causing you to get an additional combat phase after this one if it is your combat phase, along with any other mode(s) that were chosen.
Repeat from step 3.
Results
Infinite untap of creatures you control.
Infinite mana creatures you control can produce.
Infinite magecraft triggers.
Infinite combat phases.
Infinitely powerful creatures you control until end of turn.