In the 2.5D and 2D stages, you are not always able to see where you're going. Also, you see too much behind you than in front of you when running, which is too fast.
The zombie stage is just click the zombies until you get 20.
Soda stage confused me, and the bowling stage was just just 'click the reset button until it is positioned correctly'. You can also replay the level by clicking the restart button again, even after you beat it.
The crewmate stage can be cheesed.
The 7th stage is to find 'Dead eyed Dave', which I couldn't figure out, yet I guessed it right. I also guessed 'Shocked Sam' after finding Dave.
These issues make it hard to speedrun. Hopefully these things are fixed in the third build.