I played the Mythic Boss rush and got Corrupted Ancient and Ursula Windfury as final opponents. On the first turn, no treants were summoned (I did not target Corrupted Ancient), but I did kill off two of the orcs. Corrupted Ancient used an ability that dealt damage and repeated for each treant that died this turn. However, it repeated twice when no treants had even been on the board the entire turn. I suspect it was implemented as repeating for each friendly minion that died. Could the wording be updated to reflect that? Or better yet, could it be updated to only trigger for a friendly treant dying?
Looks like this was reported before.