After defeating the 2nd world boss, the game does not automatically progress to the 3rd, but you can change worlds at the start by clicking the current world icon
I couldn't reproduce the bug but just in case I added a timer to the projectiles so the will die. There are white/blue spores that are spawned by one of the towers. The damage rocks that hit them and they also are on a timer. Performance has also been improved.
A key to finishing quickly is to make sure that *injured* heroes return to the surface. Build floors so that minions/traps are clustered near the exit, and if there is nothing left to fight make sure to hit stop before the heroes regenerate. Also, make sure that your lowest level has an exit before opening it so that your high level heroes get out injured while your lower level guys are still fighting above. Your hero fees should be 150+ to start and 3000+ by day 18.
OK, actual hints for final level: Jump up hills when your bike is level at the bottom and don't plow into the last few steep hills (slow down just before them).
Perhaps a difficult slider? I found the game too easy and went all the way through without replaying anything and left quite a few missions unplayed. Seems like others ran out of XP and got stuck.
Also, are some systems supposed to be unreachable? I had some systems cut off because there was no jumpgate or further missions in the only linking sector. Without an explanation, this seems like a bug.
I couldn't reproduce the bug but just in case I added a timer to the projectiles so the will die. There are white/blue spores that are spawned by one of the towers. The damage rocks that hit them and they also are on a timer. Performance has also been improved.