I found a difference in choosing a level, starting from there and beating the level before the desired level, level 16 as an example, if you select that level and hold right earliest as possible, you will notice the spike guns will hit you, but if you first beat level 15, (still holding right as you go through the portal) you will be able to pass level 16 spike guns unlike choosing level 16 itself first, im guessing its because the game inputs your movements earlier after you beat a level, into the next level. I hope this made sense i have a problem with explaining ;-;