A few ideas:
You mentioned an energy system - if you’re willing to find a way to create it, you could try and make a stamina system that slows players down the longer they’re running. Stopping to rest (or simply not sprinting) gradually restores your stamina and allows you to run at a faster pace, but doing so will make your stamina run out more quickly… it’s all about knowing when and where to use the stamina you have effectively.
For one of the levels, you could implement a sort of randomness into the mechanics (idea mainly taken from Choonse in the Worble Cave, to be honest) and make the players faster or slower (or make their stamina run out at a different rate, or make sentries respawn at different rates, or make lasers slow you down by different amounts) based on a set of randomly changing values. To be fair, you’re going to want to make that randomness affect all players, but it also makes the game a bit more interesting - after all, now you’re not running from one end of an obstacle course to the other… you’re running from one end of the course to another while also regularly being randomly slowed down and sped up.
If possible, the level format could also follow a maze-like format that makes the player able to take shortcuts through the level (idea from Turbo Kart Racers) or confronts them with dead ends, requiring them to go back - while this does make success somewhat luck-based, it allows more experienced players to memorize the general format of each level and remember where to take shortcuts each time. I don’t know if you want to allow that kind of experience inequality to be present in your game, but if you do… that’s one way to do it.
Players could be able to attack each other, but if you do allow them to, there should be limits - maybe each player only has one shot per round, or maybe they receive additional ammunition over time. Players successfully completing the level could grant the remaining players additional ammunition in order to raise the stakes and give lower-position players a chance to knock out the opposition - players are sent back to the most recent checkpoint whenever they get knocked out from enemy/environment damage, so other players can use that against them to prevent them from completing the game quite as quickly. This mechanic could also be a toggleable setting to allow game hosts to decide whether they want PVP to be enabled or disabled.
Players could be able to collect coins or some other currency and use them to buy temporary upgrades (or powerup items could be collected directly to give players additional speed boosts, stamina, ammunition, etc - idea also taken from TKR), but you’re going to need to find a way for those items to respawn over time - to give everyone a fair chance, players ahead of the rest shouldn’t be given more advantage over those behind them.
And on the subject of slowing players down, why not make a speed game where different (easily visible) zones grant the player either very high amounts of speed or normal speed - hitting all the green zones will maintain a very high speed for a while, but hitting a red zone (or missing green zones for long enough) will result in you being set back to a regular speed until you hit another green zone. Maintaining that high speed is crucial to completing the level as quickly as possible, so the game becomes a reaction-time competition meant to see who can dodge the most barriers/zones and hit as many green zones as possible (the problem is that there isn’t really a way for you to force players to keep moving forward - ideally they’d always be moving forward and only use the a/d keys to move left and right, but in Gimkit they can just stop entirely and move around barriers at a leisurely pace instead of having to react quickly. The essence-of-speed nature of the game encourages players to keep going anyway, but still - it’s certainly something that could be improved upon).
Another gamemode could even be collaborative - players work to complete a level as a team, but still with an element of competition. Who gets the most enemy knockouts? Who actually gets to the end of the course first? You can create a game like One Way Out to give yourself an idea of how to build the map, but because it’s still a speed competition, it becomes a race to see who can take the least deaths and move through the maze as quickly as possible. Those who unlock barriers and defeat bosses first are in the front, but they make it easier for other players to catch up to them - in the end it’s really up to chance to determine who reaches the end of a finite course first, but that doesn’t mean that skill can’t also be involved! Trickery and deception will serve you well in a game like this.
There are some more ideas I could share, but I’ll probably leave it at that for the sake of whoever ends up reading this. If progress on the game is made and I can think of another idea that would fit well with the theme, I’ll try to remember to mention it then :]
