When there isn’t enough room on the board, summons from Uninvited Guest take precedence over Onyxia’s whelps, preventing them from summoning. Hero power resets as if it did summon a whelp.
Avenge mechanic is not supposed to bank its outcomes, waiting for room to be made on the board.
Same thing if you have a minion with a deathrattle that summons minions, and that same minion has reborn. One of the effects will go first and waste partially or totally the other one.
That mechanic is true for minions but Onyxia’s hero power used to resolve before deathrattles. Let’s say the board is full and with Scally’s death her hero power triggers. The whelp would spawn first, the 1/1 token would spawn second.
Oh ok, didn’t know that specific interaction.
May be a miss because of the deathrattle not being part form the base card.