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

If the same mode is chosen more than once, you choose their relative order as you cast the spell. For example, if you choose the second mode of Moment of Reckoning more than once, you choose the relative order to return the target nonland permanent cards.

If all targets for the chosen modes become illegal before Moment of Reckoning resolves, the spell won't resolve 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.

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 a spell is done resolving.

No matter which combination of modes you choose, you always follow the instructions in the order they are written.

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