Bogardan Hellkite

• WOTC Official Reminder Textofficial rules
  Flash — You may cast this spell any time you could cast an instant.

• WWizards of the Coast2017-11-17
  Official Ruling
  If some of the creatures or players are illegal targets as Bogardan Hellkite's triggered ability tries to resolve, the original division of damage still applies and the damage that would have been dealt to the illegal targets is lost. It won't be dealt instead to a legal target.
• WWizards of the Coast2017-11-17
  Official Ruling
  You choose how many targets Bogardan Hellkite's triggered ability has and how the damage is divided as you put the ability onto the stack. Each target must receive at least 1 damage.

Rulings via Scryfall