There didn't seem to be a good move to make here. For example, Iron Man took the chance to take a few more steps into the room while the demon had its back turned, only to freeze as it rounded on him again, not sure what it meant to do with a knife until-- well, okay, Tony was having a hard time keeping up with the patterns here, but what a total psycho did was quickly becoming familiar, thanks. He jerked forward as Wanda started to fall, heel slipping in the gore and making him catch himself while the demon righted its body. It was probably good that knife stayed there anyway, lessen the blood loss, everything was fine.
"Here's the thing," Iron Man observed, hands up in surrender, "I'm getting the sense that it doesn't matter what anyone does, you'll hurt her," like just innocently standing there, "so let's work away from that theme. As far as I can tell, that body is yours now and Wanda's just taking up room in there at this point. Is that about right? So, if you follow me, it might be in everyone's best interest to get her out of your way?" Maybe not an ideal situation, Tony did really like that body, but at a certain point you stopped taking the car to the shop and you looked into a new model. Like when it was completely totaled by a megalomaniacal bad driver. "I don't know anything about demons," Iron Man admitted, apologetic hands on his chest, "you'll have to help me out there. I mean, you got yourself in here, so..." Surely, the process wasn't so different.