This is really well done for a jam game, great work! I got a bit addicted to playing around with the movement mechanics- even though you're not the first to make a game like this (e.g. SpeedRunners), I still had a blast experimenting with it all. Here is all of my feedback:
- I agree with what a lot of other people have said about the collision & momentum issues, it feels unfun when you stub your toe or let go of a movement key and instantly lose all momentum. You're probably already making use of coyote time, but I think there are a lot more opportunities to 'cheat' with the inputs to make them feel player-friendly, for example by slightly delaying the character's hitbox shift from sliding->standing so they can still slide under a wall if they just let go of the button slightly too soon. I also think it might be better if the player didn't fall like a brick when letting go of the jump button, and was more floaty instead, with a separate button (s/down) that would let you fall fast/dive/slam/etc.
- I love the physics interactions you can have with ramps where you can build a ton of speed if you hit them just right, and would love to see maps with rounded slopes/halfpipes that the character could run on or slide down almost like Sonic. The more options, the better! And keeping the options generic enough/scalable is a great idea so they can all work within your level editor once that is complete.
- You mentioned that you were working on a fast restart that would skip the intro cutscene - this is a great idea, but it might be better if the skip would just happen automatically upon player input, as long as it hasn't been skipped at least once.
- Speaking of player input, I wish the game would keep track of my inputs outside of their relevant game states so they could transition immediately when possible. For example, if I hold the slide button while in the air, I want my character to slide right when they touch the ground instead of requiring a second input. When I restart the level, if I was already holding the right arrow button, I want the character to start running right instantly.
- I love the idea of the level editor, but I also think you should have a set of official levels to choose from, to teach the player the game mechanics, give 'base' options for players that can guarantee a good play experience, and to act as a guide for people when they venture into make custom levels (like Mario Maker).
- The concept of chasing down a previous version of yourself is very cool and is what makes your game fit the role reversal theme in the first place, but in all honestly I don't think it's that well implemented currently. At present, it just means a speedrunner would have to slow down for half a second at the start of each run to guarantee that they would catch the ghost at the finish line. I don't know a perfect solution to this problem, but here's one suggestion that might work:
You could make it possible to go 100% full speed throughout the initial run, but have map obstacles that change in a predictable way once the finish line is reached, so that your future self has some options to catch up without having to intentionally slow down. For example, doors that open up, walls that slide to one side, speed boosts that become active, level inversions, and so on (the ghost doesn't necessarily have to react to these changes). You might also consider allowing the player to chase their past selves indefinitely so long as they are within a distance radius. So if you mess up slightly in your chase of a perfect past self, you're not necessarily out of luck even if the finish line is passed, as long as you can keep up within reason.
At first I thought it might also be a good idea to count the chase sequence time as part of the total time in the leaderboards to reward players who do well in both phases, but that would only work if it's not possible for speedrunners to get a better overall time by doing poorly in the first phase, so maybe keeping the total time as a secondary non-ranked stat would be better. - If you are open to expanding the scope of the game in future versions even further, I think it would be absolutely fantastic to build in a real-time multiplayer feature, as that is always a great time for these kinds of games and is very likely what would draw in a lot of new players who otherwise wouldn't be interested. There are a lot of interesting ways you could implement multiplayer, whether it would be a co-op only thing, or a lobby system with anywhere from 2 to 100 players, possibly with different gamemodes that all have their own implementation of the assassin phase shift concept. I'm imagining some crazy scenario where you could have 2 teams of players that get to take turns shifting between the assassin team and the runners team while both are playing simultaneously, there's a ton of potential for sure.
- I would love to have the option to either race or chase down a player's ghost from the leaderboard, or my friends' ghosts.
- A nice minor improvement to have would be an options menu with the ability to go fullscreen, and a game scale slider. I'm playing on an ultrawide monitor which this game could definitely benefit from if it would take up the extra space!
- Generic controller support would be very appreciated as well.
Overall, this was a great experience!