Straighten a Twisted Outside Corner Without Carpentry

(This is a bit off-topic but...)

The carpenters that added a new closet to this room either didn't notice or didn't care about the bad twist in the framing lumber.
I didn't notice this until I had started to tape.

Compared to the new, the old wall looks worse than it did.

Tape that joint (the worst place for a drywall joint) , then screw a plastic-lined drywall scrap to the adjacent side. This serves as a mudding guide.

With this guide in place, the outside corner can be built up and out square and flush with drywall mud.

(The plastic stops the mud from sticking to the scrap drywall).