You can spawn him with one character under invisibility, the spell won't break. At least it didn't for me, might be a bug?
When spawned, the spectator just started unpetrifying and killing the drow and my character was waiting for their battle to end under invisibility. I thought the spectator would win for sure but somehow the drow managed to beat him with only one of them left standing with low hp. He must have felt really proud and lucky... until I eldritch blasted him to his death from behind
By the way, was anyone able to talk to the drow using Speak with Dead spell? I couldn't do it even though I didn't kill them myself (well, except for that one last dude).
