Are you planning on doing custom animation for the Combat Cross or what? Do you have any concept done for it yet? That's the most interesting thing I want to see how you plan to incorporate in the mod. I am still suggesting you look at how the grappling is done in bionic commando and then use that as a base to fix it for your needs. Then you could incorporate some vertical climbing in it similar to Lords of Shadow.
lords of shadow's level design is pretty garbage, and wouldn't translate well to a 2D game. and yes, the combat cross will have a custom animation. the belmonts soul is a single, powerful foreward attack. the combat cross is for players that would rather be 'faster and loose' i guess. it's got wide attacks, and attacks in a six directions, it does a lot less damage though but also comes with it's own set of abilities
i like the 'concept' of a swing in combat, but it's not something that would really suit this game. if i do another castlevania game (maybe using thaddeus' richter sprites that i made a full sheet of) i'll consider it
a good example of the kind of things Combat Cross!Richter can do, is he has access to a back handspring/dodge like leon/alucard/soma/juste do, while Belmont Soul!Richter, has access to subweapons