First thing you must do is push the boulder to your right, all the way until it is over the balloon, it must be exactly over the balloon, you’ll find out why later. Now go all the way left, go down past the spike gate, all the way down, go two right, then up collecting all the diamonds. Then go down and push the balloon to the right, go up two and all the way right, lighting the two stacks of TNT.
If you want full points, go on the left side of the three chests and get the middle first, then the top, leave the bottom one for now. go one left and quickly down, lighting the TNT. Collect the extra key next to the yellow balloon and go through the chest underneath the spike gate, light the TNT and quickly press down as far as possible.