Today I was fooling around a bit using some game genie codes taken from
Gamehacking.org. Specifically the invincibility code BWST-AA26, and the high-jump code RGRT-A6YY.
Did not find anything useful while having the codes activated, but I did however find some oddities. I knew some places since before where you can enter the empty voids outside of the screen. What I did find today however is that they are actually connected somewhere else. Not that we have any use for it since it runs in the wrong direction. I thought I post about it anyway for the purpose of knowledge, and who knows, maybe we find something useful later?
In level 2-1 for example there is a gap right above where you start. Jump up to the right.
Also. At the exit sign in level 2-1, jump to the right and you'll fall down the shaft ending up under the trampolines
Besides that I thought of a shortcut in level 2-2.
Right after you get the flamethrower it should be possible to manipulate the enemies in order to skip upwards and reach the second elevator. I was close to manage it earlier today but the great flying demon would end up spearing me to death. In order to make this I used the flying fish. Avoiding it instead of killing it and try to bounce off of it in order to reach greater heights. Also for that to work I think the first elevator needs to be at its peek height, or close to at least.
Here is a poor illustration (also, the fish did not make it for the screenshot):