Some of my ideas:
- Character customization
- A results screen for speedrun mode showing how long each level took
- Saving your PBs for each level (including speedrun mode)
- The option for choosing either pre- or post 0.7 physics engine
- Like/dislike system for custom levels if they come out
- Epic & my favourite idea: hard mode for levels, making them harder to complete
Edit: By hard mode I mean: same animal, but... changed on the inside
Edit 2: It says: C A S T L E