Matthew would also get involved in this (although after what happened to Malik and especially after he hears about Armin he is basically going to insist that they all need Multiple Escape Plans for this).

In terms of useful skills, he has: Teleportation III, Summon Traveller, a gazillion other portal skills, Eldritch Defence, and Bando Summoning / No Distinction. Not sure if fire elementalism would be useful considering that the poltergeists didn't react to it before, but on the off chance that it does, he has that too.