If you choose new targets for the target spell or for the copy, the new targets must be legal.
Insidious Will
If the spell has damage divided as it was cast (like Chandra's Pyrohelix), the division can't be changed (although the targets receiving that damage still can).
The copy will have the same targets as the spell it's copying unless you choose new ones. You may change any number of the targets, including all of them or none of them. If, for one of the targets, you can't choose a new legal target, then it remains unchanged (even if the current target is illegal).
Magic: The Gathering · ™ & © Wizards of the Coast · Illus. Anthony Palumbo
Card data via Scryfall. Rarix is fan-made; not endorsed by the rights holders.
