@BeezyLoove There would've been a Halberd level as seen in some footage. We can also speculate on possible sub games that could've appeared from the menu concept art. Cracked star for the Dedede steals the Warpstar mode, M for RoMK esque mode, sword with bat wings for Meta Knightmare, etc.
@PolliePhantom It almost 100% was. The textures for its model in RTDL use a "bs_" prefix which is the same prefix HR-D3 has for its textures (As well as Kracko and Dyna Blade's trophy textures from Brawl) and we know HR-D3 was reused from GCN. It also has a bone in its model named "BossCenterJ"