All right! I wasn't expecting this one. So, that body's consumed a mirror aimed against Anurr's branch of undead, meaning it shouldn't really affect Unhalad's people. But it could act on the communal thread of these dead, which is effective possession — and you're bringing an already weakened possessed body.

Let's call it your pick: if it's an incredibly "thawed" miner (as most of Unhalad's forces are miners), you can choose to have them die if they enter the lake and spend too long in it. Alternatively, you can choose to have them stay away from the lake and remain unaffected.

Either option works, up to you how much you want to traumatise your boys. Just let me know which way you want to go, please, so I can work that into future updates!