The 'Monstrous Takeover' Battle Tactic from GHB21 requires you to "pick 1 MONSTER from your starting army on the battlefield" to complete it.
How would this line up with the 'Metamorphosis' spell which gives a a hero that isn't a monster the MONSTER keyword? If I gave a hero from my starting army the keyword during that turn, would the hero be eligible to complete the BT? Or would the unit have to be a monster from the start?