Great Train Heist

You must choose at least one of the listed modes and pay its associated additional cost in order to cast a spell with spree.

If a mode requires a target, you can select that mode only if there’s a legal target available. Ignore the targeting requirements for modes you don’t choose.

Notably, Great Train Heist’s first mode doesn’t give you any additional main phases. This means that you will move directly from the end of combat step of one combat phase to the beginning of combat step of the next one.

If a spell with spree is copied, the effect that creates the copy may allow you to choose new targets. You cannot choose new modes.

No player can cast spells or activate abilities in between the modes of a resolving spell. Any abilities that trigger won’t be put onto the stack until the spell is done resolving.

If an effect allows you to cast a spell with spree “without paying its mana cost,” you must still choose at least one mode and pay the associated additional costs.