There are couple cheat codes that are fun and some that can be really useful for routing and practice.
• Big Head Mode
Hold DOWN and jump/press A. While in the air, press and hold UP and jump/press A again. Press and hold DOWN in the air and, then hold UP and jump again, etc. Repeat this DOWN-jump, UP-jump three times and you enable Big Head Mode. Repeat the same come to revert to normal Lizard size.
• EASY and Soundtrack Modes
Press SELECT on the title screen to bring up an options menu enabling you to select easy mode, turn music off, or enter a Music Test to listen to the soundtrack without playing.
• SHART mode
idk what this really is or does, but in the options menu if you press B the title screen says PRESS SHART instead of PRESS START.
• SWITCH LIZARD ON PAUSE
Pause the game and enter RIGHT, UP, DOWN, DOWN (RUDD) and hold the second DOWN input, then press SELECT. This will unpause the game and you'll be the next lizard power. It's sequential in order (knowledge, bounce, swim... I forget the rest of the order)
• DEBUG MENU / DIAGNOSTICS ZONE
Pause the game and enter DOWN, UP, LEFT, LEFT (DULL) and hold the second LEFT input, then press SELECT. This will transport you to DIAGNOSTICS ZONE. Here you can fiddle with various settings about the game.
It shows your current IGT, deaths, jumps, coins collected, and continues (aka the times you used the warp/password door).
You can also mark which coins have been collected and certain game flags. Use the SELECT button to toggle between COINS and FLAGS. Use UP and DOWN to select the memory address (00-7F, aka 128 potential coins and flags each). Then jump and git TOGGLE to swap that memory space to 1 or 0. Each pair of s represents 1 byte.
For example, FLAGS 0A,0B,0C,0D,0E,0F represent the bosses killed and light the torches that open the final boss portal. Set these all to 1 and you can enter the final boss.
(I'm working on mapping which COINS and FLAGS represent so hold tight!)
• WARP TO ANY ROOM
So technically you can warp to any room with any lizard costume using the password screen. The game naturally only shows you the password for the room of the last save point you hit and with what lizard power. If we ever reverse engineer how the password system works, you can warp to any non-save room by holding SELECT+A, then pressing up on the password door. I've tried random codes and gotten to non-save rooms with this method.
This can be useful for practice once we figure out how the codes work (i.e. warp instantly to a room with the desired lizard power instead of walking all over the place)
• BOSS RUSH MODE
Enter password 32186. This takes you to a room with three bosses, and a door to the other three. There is also a toggle switch to pick any lizard power. Each side also has an entrance for the final boss rooms. This code can be gotten naturally by being the vanilla game quickly (I've gotten it with ~25mXXs IGT; maybe it's under 30 minutes).