I realize this game has not been active for a while, but I stumbled upon an out of bounds to get on top of the map on the way to the Zolthan boss fight which you can use to wrong warp to various rooms. In most of the rooms you are stuck on top of the map and a lot of the warps crash the game, but I found one that allows you to backtrack all the way to the top of the first main room of the game. Based on the current 100% record it looks like this could be useful after beating the third boss when you backtrack to get the extra collectibles near the beginning of the game. Here is a video of the trick with input display:

I guess it is also worth noting that you can also come back in bounds in the second boss fight room, but I don't think that is useful.

Ooh, this looks like a cool trick! It's been a while since I've done any speedrunning, but I'm excited to try this out.