~blinks~ I didn't know that finales did that if you are using one of the participants in a joint finale as a player avatar. That's... interesting.
As for Lord Octo, well, actually, clothes are available for him, so it would be possible to create a player only character out of him. I'm not sure how many people would want to play him, or identify with him, though.
As for the special finales regarding him, or any other player-only character, that would be a little trickier. At my last count, there are nearly 50 opponent/outfits now available. That's a lot of finales when you multiply them by the player-only options. I also believe there is a game policy of generally not including player-only character finales. Lord Octo is acting more as a prop for Mary rather than a character in his own right. So player-only character finales are a policy decision and that means it's in Eldricus' territory. ~Throws the hot potato in Eldricus' direction~