Not much to say here, toggle-able ghost costumes in editor to help you trace/match frames right.

In detail: http://prntscr.com/1vutr1
The ghost effected sonic is the onion skin, it is a transparent clone of the previous costume.
The non-ghost effected images of sonic are a sprite sheet, and the onion skin will assist in lining it up right to make the animation work.
Another example: http://pivotanimator.net/help/images/onions_run.PNG
Again, the ghostly duplicates only appear in-editor, but not in the final animation itself.

Thoughts on the idea?

Nice to see the first reply is a point-to-duplicate… never saw the other one. I was just trying to do some spriting and came across the thought of suggesting it.

DJEnderman64 wrote:

Nice to see the first reply is a point-to-duplicate… never saw the other one. I was just trying to do some spriting and came across the thought of suggesting it.

And a great idea it is too! However, since we already have a topic on it, let's please use that one.