To unlock secret levels and modes, link Crash Bandicoot 2: N-Tranced to Crash Bandicoot: The Huge Adventure.
Get a 100% completion by collecting all crystals, gems, gem shards and relics to unlock level 40 and another Boss. Successfully complete the bonus level and defeat its Boss to get a 101% completion.
When you are at the end of the level in time trial mode, when you see the three boxes and the arrow pointing down the ramp, do not follow it. Continue in the way you used to reach it until you see the green gunk and the path. Go on to the path (hold A and use the D-pad) until you see the end with the ramp below. At that point still go forward you will be guaranteed to land on the ramp, only if you do not make a mistake.
When you get that puppet mask floating behind Crash, press Start and go to the Warp Zone. When you go to the Warp Zone, notice that you have the Puppet Mask floating behind you. Then, go to a level and do not die or lose the puppet. As soon as your puppet mask gets yellow (from getting the puppet crate), press Start and go to the Warp Zone. When you get out. you are in the Warp Zone again with the yellow puppet. Go to any Boss that you are having trouble with. It will easier because you have enough power to survive two hits. This trick works well with N.Tranced.