Stumpsquall Hydra

• WWizards of the Coast2020-11-10
  Official Ruling
  If Stumpsquall Hydra leaves the battlefield before its triggered ability resolves, you can still distribute the counters among any number of commanders, including none of them.
• WWizards of the Coast2020-11-10
  Official Ruling
  Because Stumpsquall Hydra's ability doesn't target, you choose how to distribute X +1/+1 counters as its ability resolves. Players can't take actions between the time you decide this distribution and the time counters are put on the appropriate permanents.
• WWizards of the Coast2020-11-10
  Official Ruling
  You can't put +1/+1 counters on commanders that aren't on the battlefield.
• WWizards of the Coast2020-11-10
  Official Ruling
  You may put +1/+1 counters on commanders that aren't currently creatures (such as Tevesh Szat, Doom of Fools).

Rulings via Scryfall