Is it fine if i post ONLY the stage graphics, which seem to be the only assets in the game that's original (for the most part)? I feel like we should also have a rule similar to M.U.G.E.N in that we should only accept assets from the original unmodified game (and in BOR's case, the Neo Edit Pack).
Not a staff member but personally there shouldn't be anything wrong submitting sheets as you gave a good reason.
Yeah, it's fine to rip the stages and other assets well providing that they are indeed original and not from other games.
Like MUGEN, it is no longer updated by its original creators. The game/engine is even declared freeware and open source so chances of the sheets being taken down are very slim (still possible though but
the original developers are no longer involved with it).
Yep, "vanilla" content is perfectly acceptable to submit.