I need playable incorporeal creatures for nefarious purposes

[TheArcaneWeirdo]

So. The first arc I was thinking about for my campaign is this:
The party is a group of teens from Toyalis, who are good friends. A while ago, three of them were taken to The Red Academy - two as students, one as a lab rat. The students realised what's going on, and on their first weekend off, had reunited with their non-magical friends and started plotting something very brave and very foolish:
To infiltrate the academy's secret laboratories together, find their friend and rescue him - all beneath their teachers' (and a bunch of aberrations') nose.
If they succeed, they'll find him already somewhat changed by the magic he was exposed to - but very much still their friend.
I was thinking about making the friend a PC rather than merely a victim - mostly because I thought it would be a cool backstory for a Reborn character - but then, how do I give him agency and make the arc fun for him?
So I thought about temporarily separating his mind from his imprisoned body. Letting his ghost or his astral projection or something participate in the ploy to save himself.
So, what would be a good option for that? One designed to be playable? In 5e.

[Wolfglide of the Fraternity]

I played this homebrew ghost class in a game once:
https://www.dmsguild.com/en/product/226 ... ath-option
I only used it at 20th level, and it was a long time ago, so I can't speak to the particulars of it, especially for a lower-level game, but it was written by Matthew Mercer, and it's Pay What You Want.

[TheArcaneWeirdo]

I played this homebrew ghost class in a game once:
https://www.dmsguild.com/en/product/226 ... ath-option
I only used it at 20th level, and it was a long time ago, so I can't speak to the particulars of it, especially for a lower-level game, but it was written by Matthew Mercer, and it's Pay What You Want.

I'm checkng it now, sounds great