Camel drew lots of underwater stuff at one point involving Milia and Sachiho, including lots of concepts for underwater enemies. An underwater stage would be interesting.
One thing I've always wanted to see them do was a boss which is the stage/environment itself, that is, a giant fleshwall room, where, upon being swallowed, the player character would be vored in various, random ways, from travelling along tubes, being deposited into stomachs, pods and sacks of various kinds, pools of liquid or slime, and so forth. The Demon Womb stage from Splatterhouse comes to mind where the whole stage is made of flesh which spawns enemies.
Another thing I'd like to see added is an option in free play to have waves of enemies spawn, though this could be it's own game mode. I'd like to have the game generate waves of enemies on it's own without me having to select them each time in free play. One thing they could do is either have you choose what's in the waves yourself or have the game randomize them, either from a list you have chosen or from the entire list of monsters.
Being able to choose lives and to add a timer would be nice too, I have to make my own rules externally with Free Play, using a google stopwatch and a text document to keep track of lives. My own personal rules in Free Play are
- Survive for 10 minutes
- 10 lives
- Maximum enemy spawns(20)
- No combos(only single hit attacks)
- No ranged, ducking, aerial or special attacks
- 3 second cooldown on each attack (as in I wait 3 seconds before being allowed to attack again)
- Double-Jump only (so no multi-jumps for Miria)
- Clearing all 20 enemies gets me a life back
- Enemies are replaced with another 20 enemies when the previous wave is cleared
- 2 enemies re-added whenever I am KO'd
- Victory condition is met when the 10 minutes are up and I clear the screen of the current wave of enemies
Another way I play is to have a bunch of enemies and I am not allowed to attack until 5 minutes pass, so I have to dodge the enemies until the 5 minute mark, at which point I can fight back.
