Jugan, the Rising Star

• WWizards of the Coast2017-11-17
  Official Ruling
  If some of the creatures are illegal targets as Jugan's triggered ability tries to resolve, the original distribution of counters still applies and the counters that would have been put on the illegal targets are lost. They won't be put instead on a legal target.
• WWizards of the Coast2017-11-17
  Official Ruling
  You choose how many targets Jugan's triggered ability has and how the counters are distributed as you put the ability onto the stack. Each target must receive at least one counter.

Rulings via Scryfall