Pretty sure it’s not Excitebike, but I’m going to guess it anyway.

A boy and his blob

Never had a Game Boy but my friend had one. I only ever saw two games on it, Tetris and whatever Mario game came with it. So I’ll say Super Mario Land.

I already guessed Super Mario Land… It’s not that…

Mmmm, I know I have played this game, but can’t remember it.

Nor is it Rainbow Islands.

Nobody guessed it yet.

Flood?

Donkey Kong? Gameboy version? It was quite different from original DK versions, if I recall correctly. That umbrella is so familiar to me. Got it confused with the one in Kid Dracula.

Such a brilliant game.
It started with the classical 4 levels of arcade gameplay, before surprising the unaware by switching suddenly to one of the best action-puzzlers ever made.
My experience with cartridges has been poor though: I bought this game 3 times, and every cartridge have had their internal battery fail - I strongly suggest emulation for this one, if you haven’t played it yet.

Congrats, Kyosho!

Alright. Let’s see…

Spelunky

I can tell what it is, I just don’t know where it’s from.

King Arthur’s Gold?

Nope nope. I have a feeling this might be a difficult one. Not actually sure.

Axiom Verge?

Nope. Also, just to help a bit, since this might be a hard one… The aspect ratio is important. This game cannot do widescreen natively.

Have we done Cave Story yet? Because that’s my guess.

Delve Deeper?

Nope nope.

Gynoug?

Nope, but in one way, you’re getting warmer.

Rastan?