well some ideas i had for level objectives are pretty basic, stuff like:
- find an elevator key
the elevator key is attached to an enemy. you'll need it in order to leave. if you just go for the key you can skip the level, if you just kill every bot you're guaranteed to get the key (check if player has a key when player is near elevator, unlock elevator) - survive for # time
enemies would continuously spawn throughout the level. you could try to clear out all of the enemies so there's less threats, or just outrun them until the time runs out. (wait # seconds, unlock elevator) - survive # waves
enemies still continue to spawn after the level starts, but instead when all the enemies are killed, more enemies spawn for a new wave. this is a bit of a roadblock objective. (maybe add a slight grace period) (repeat until #, unlock elevator) - kill big bot
instead of the normal enemies, you have to hunt down a more dangerous bot. this can be a souped up enemy or, if there's bosses, a somewhat lite version of a boss you've already defeated in the run. (if big bot killed, unlock elevator) - this elevator has reached it's destination
this is more like a secondary objective, you will need to find the other elevator in order to continue, but also you still need to complete the level's objective