You choose the modes as you cast the spell. Once modes are chosen, they can't be changed.

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. Each time you select that mode, you can choose a different target, or you can choose the same target.

No matter which combination of modes you choose, you always follow the instructions of a Confluence in the order they are written. If the same mode is chosen more than once, you choose their relative order as you cast the spell.

No player can cast spells or activate abilities in between the modes of a resolving spell.

If a Confluence is copied, the effect that creates the copy will usually allow you to choose new targets, but you can't choose new modes.

If all targets for the chosen modes become illegal before the Confluence resolves, the spell will be countered and none of its effects will happen. If at least one target is still legal, the spell will resolve but will have no effect on any illegal targets.