Rommy, could you please add the script for c3m5, where the alternate upgrade from Isabel triggers, and share it here? I don't know how to do it myself. I hope they don't run off to Godric and join him (the video says so), otherwise they'll end up in his army. I might finish the mod in a few days, but it's not certain.
I came up with two options: in the first, the third alternate upgrade triggered correctly, but the notification window didn't appear; in the second, the notification window appeared, but it randomly said that the griffons had left, while in reality, it was the archers. Neither option is very good.
I think it's better to give up on it; no one will play as Isabel in this mission, at most for the first week to capture the mines; all the human units will end up transforming into undead anyway.
Or, someone who is good with scripts could help.
Also, it's likely that new text for the third upgrade's tooltips will need to be added.