Don’t know if it’s the right topic to discuss the GBC version of this game, but I’ve finally played the secret Ubi Key level of this version and made a showcase of it!
Basically, this extra stage makes you play as Super Ed (with no time limit) and makes you go through a unique area with instakill enemies falling from the sky and a bonus life at the end of it.
Here’s what I discovered:
-While the creatures kill you instantly, you can do the same to them by punching or kicking.
-They only spawn outside of the starting area and of the life’s location.
-You have three attempts in total (like your default number of lives). You’ll be sent back to the game’s intro regardless if you win or if you lose.
-The extra life actually counts as
three, as you’ll start the game with six lives in total.
-There’s no HUD in this level and it simply uses the game’s main theme.
-There are some "glitched" visuals under the stage. By moving the camera downwards (which you can do by repeatedly tapping the up and down arrows), you’ll see broken tiles below the whole level. Funnily enough, Super Ed also floats above the water here when walking across some platforms...
-Most interestingly: it appears the creatures change depending on which game the Ubi Key has been sent from (unless this is completely random, but it was consistent in my many tests). Sending the Ubi Key from a second Tonic Trouble will spawn tomato enemies, while sending it from Rayman GBC will replace them with yellowish versions of the Pyramid’s jaw creatures (could be a reference to the Piranhas from Rayman?). Does anyone has more Ubisoft games with the Ubi Key feature to test that out?
Once again, I’ve detailed the whole method in the video’s description as it was quite tedious to do with emulators.

(Especially when it keeps crashing because of the IR + netplay features

)
Guess I should update the wiki page soon like what I did for Ubi Cliff and Rayman GBC! Well, with the confirmed information as I have some doubts about the last thing.
Here are pictures with some details:
(The Ubi Key menu. The GBC with the arrow pointing downwards is to receive the key, while the other one is to send it and is only available if you find the Ubi Key in Vegetable HQ’s first level)
(The enemies I saw when sending the key from Tonic Trouble)
(The enemies I saw when sending the key from Rayman)
(The weird tiles)