This is sort of snow idea I've had recently, though now that I look at it I'm not too sure it is terribly original.

My thought is what if in an alt universe (or something else entirely) instead of banishing monsters to Tartarus, the Moon or turning them to stone, they were Turner into a metaphysical form and placed inside of other ponies who would serve as "vessels/containers" for these beings.

It isn't like possessing exactly as the pony is still in control, however they might exhibit traits of the being the contain. For example a mare serving as the vessel for Tirek might possess similar horns.

Just thought I would throw this out and see what you all thought.

That would be quite interesting...
Would our lovely squad of six also be acting as “vessels”?

6701936 It is possible. On the other hoof, I could just wait until the next Gen comes out and implement this concept with the main characters from that (if it's any good).

Eehhh I don’t like how the next gen looks...

6701944 I actually haven't seen the next gen. Did it get leaked or something?

Yes
It was