I don’t understand what you’re trying to re-target.
Which animation do you want to retarget? Which skeleton was it built for? Which skeleton do you want to re-target it to?
I don’t undetstand the “problem.”
If you have an animation that animates a cape, or wings, then those bones can’t be targeted to the base mannequin, who doesn’t have those features.
If you have an animation for the base mannequin, then that can’t animate the cape/wings, because the mannequin animations don’t have that movement.
The only case you need additional bones, is when you have mesh A, which has a cape or wings (thus, not the default mannequin,) and you want to target mesh B, which also has a cape or wings (thus, also not the default mannequin.)
And, because the default mannequin is not involved, then you don’t need to use Epic’s rig for that re-targeting; you can use a rig that contains the correct number of bones (typically, the rig of the source character.)
What you seem to want to do, is be able to:
- Take an animation from a winged character, and re-target it to the mannequin (which does work!)
- Then take that re-targeted animation, and re-target it again to a winged character, and somehow make the animation data for the wings follow through.
I don’t think anyone expects this to be a workflow they will use, and I don’t think anyone expects that that would work.
That’s what I think the Unreal reviewer meant when he said you’d be fine.