to complete with minimal deaths:
4-1 -- hop across the top once. Grab the key. hop across again. grab that key. Hop across one last time, and you're done.
1-3: notice that you can push around corpses while you're standing on them. Well, that's exactly what you'll need to do here. You'll need to literally surf across the pit of spikes on top of the bodies of one of your dead 'friends'
The levels that you're required to die at least once on are: 1-3, 1-4, 2-2, 3-3, and 5-2.
TIP: When going for maximum speed, do NOT use all your rocket fuel in the beginning! Without rocket fuel, you'll only reach a maximum falling velocity of around 319 when falling. The key is to use whatever rocket fuel you have left at around a speed of 310-320.
I play the green hill zone in the background whenever I play this.
Why?
Because I believe.
(...and because i'm playing the sonic game while this is stuck going right in the background from holding right and clicking on another tab o3o )
for those that are having trouble using the keyboard:
Position your dominant hand sideways, and hold your thumb over the spacebar, the index finger over the N/V key, the middle finger over the J/F key, the ring finger over the O/E key, and the pinky finger over the 0/2 keys.
Finger name reference sheet for the confused: :P
http://www.programmingart.com/products/key/keymanual/images/handsForManual.gif
Yellow AI: hmm...I have a blue enemy right next to me. it would be easy to take him out! well....ahhh forget logic, ima going to aim for that red guy 500 feet away from me! :P