Crash Bandicoot 2: Cortex Strikes Back/Night Fight

This level is completely dark and the only way to temporarily illuminate the area around you is to catch some fireflies you find along the way, which will follow you for a certain distance. You have to be very quick though, because after a few seconds the fireflies leave, and you must therefore make sure you reach another firefly before remaining in the dark. Along the way you will have to overcome gaps and defeat some enemies. At the beginning you will only encounter simple mice, but later enemies that you can only defeat with a slide and indestructible flying robots will also appear. Around the middle of the path you will find the crystal and at the bottom you will find the detonator to blow up all the Nitro boxes.

The bonus area is located just beyond where you took the crystal and follows the same logic: you need to catch fireflies to light up the area around you and move quickly to reach the next firefly before it leaves. Breaking all the boxes isn't difficult, but at some point you'll need to use your sliding and crawling skills to get under some Nitro boxes.

Getting the first gem
About a third of the way through, there is a fork in the road. The normal path is the one on the right, but in order to take the left path, you must get to this point without losing any lives. You will thus find a platform marked by a skull that will allow you to overcome the abyss on the left and continue. This area, as usual, is more difficult than the rest of the level, but along the way you will find the gem to collect. The two paths later rejoin.

Getting the second gem
To break all the boxes, your best bet is to go right at the fork, ignoring the platform with the skull. When you get to where the two paths rejoin, quickly backtrack along the left path, walking towards the screen. At this point you will certainly already have a firefly with you, which should be enough up to the point where you will find two boxes and another firefly. These are the only boxes in the path to the left, so break them quickly, grab the firefly and head straight back, continuing the level as normal. In the final room you will find the gem, provided you have broken all the boxes in the rest of the level and in the bonus area.