Jund Charm

• WWizards of the Coast2008-10-01
  Official Ruling
  While the spell is on the stack, treat it as though its only text is the chosen mode. The other two modes are treated as though they don’t exist. You don’t choose targets for those modes.
• WWizards of the Coast2008-10-01
  Official Ruling
  You can choose a mode only if you can choose legal targets for that mode. If you can’t choose legal targets for any of the modes, you can’t cast the spell.
• WWizards of the Coast2008-10-01
  Official Ruling
  If this spell is copied, the copy will have the same mode as the original.

Rulings via Scryfall