So I finally found which game it was. Actually that does depend on who made the trainer. Or is it my disk that has a soul? Hmm. If that's the explanation then now that soul is available for the spreading n_n
Just kidding. I was almost certain the game was Dragon Breed, but downloading an image on the net gave me this trainer:

F3 cycles between 1 and 6.
*Grunt*
So, just to make sure I'm not wrong about this game (was not 9when I found this trick), some deep investigation must be carried out n_n
Ok, start at stage 6.
Jeez I died like 40 times before reaching the end of it. How could one play 6 levels + the "boss" ones with three lives? Off topic, ok.
So, when level 6 is done, you reach this bouncing dude with some eyeball above his head:

He finally dies:

Aha! Now, do I get to level 7?
Answer: no.
You get a nice ending screen:

Well, nice is relative. Whatever.
Then ... surprise?

Actually if you see this screen, I suppose it means: "based on the hypothesis you've started with level 1, you've seen all you had to see in this game. This is the truth."
-> geeks will add: "what truth?".
So. Back to my box-o-floppies. Hah! The damaged one with the worn label "dragon breed":

MSA2.3 in action (yeah I show this because it was a pain to figure out how to make a simple image... my dreadful 486 (my only computer that still has a floppy disk. Beware my 486) and makedisk failed to read sectors. I suppose it's due to the 10 sectors issue?)

MSATOST made a gread job to combine the two files. Yay. And 486DX4-100 are excellent machines.
Ah. Now that's the trainer I remembered:

Do be fooled, it accepts input from one to nine. Also attempted hex a, b and co but only three "hidden" levels available. Jeez was proud of my discovery, I remember that. Was young, too. Hehe, my age could nearly be coded on three bits.

Hey look at these weird things.
Stage 7:

Wow you meet a strange egg.

Inside it a crab awaits. Poetry.
Please not the crab has rude manners and throws buggy textures at you. Nasty crab.
Note: If you get killed, either the ST crashes (no even bombs, just reboot), either the egg will be "frozen" and will have "god mode on".
Stage 8:

Connoisseurs have harmoniously dubbed this level: "it came from the toilet". Haha.
Notice how it throws up some buggy textures. The eyes are also composed of buggy textures, which make this whole level feel like a kind of unfinished business sanctum. Initiates only, are we?
Don't get killed by the poo tower, or else you appear cursed in the middle of it (and die btw):

Stage 9:

This one will beat the poo out of you, for sure. Perhaps the initial "boss" at the end of level 9. So tough that it's maybe been replaced by the blue freak with his eyeball pet.
Ok, Voilà!
Guess what's next? Voilà! In view, a humble vaudevillian veteran (...)
Oh, the file:
http://www.filefactory.com/file/2b3114/
You don't need an account to download it, just pass a picture-with-text-inside-test. The link to download it is at the bottom of the page. Ta-ta.