I had some problems with running this game. The browser version failed before the game even started (on both Firefox and Chrome). I downloaded the ROM and tried it with a few emulators I had installed. NanoBoyAdvance kept giving "Invalid graphics index: -1" errors everywhere, and BizHawk (which uses an mGBA core for GBA games) wouldn't let me access the settings and randomly froze. I finally downloaded the mGBA build you included on your itch page, which seemed to mostly work. Making a game jam game for the GBA is really ambitious, but seems like your game has a lot of technical issues because of that.
As for the game itself, I like the idea, but the execution has a lot of issues for me. For one, the snake's behavior seemed really unpredictable. It was hard to try to formulate any sort of plan because I didn't understand its behavior, which meant it felt more like I was getting lucky than winning because of my actions. Also, I'm assuming the snake moves before the player, because there were times I felt like I should have been able to narrowly sneak by, but the game disagreed. This feels way more unfair than giving the player's movement priority.