That underpromotion 

Nobody solves that.

that has to be the most stupid thing i've ever seen, could someone please explain to me what i just saw?

that's a bit different kind of puzzle.

Check the "Move List" for explanations of the underpromotions.

Spoiler:

There are several stalemate tricks possible. In general, if g5 and the h-file are covered, black will draw with underpromotion to knight on f1.

And in the end most computers will not understand that white has to keep the rook imprisoned to prevent sacrifice against g-pawn with drawn "wrong bishop" ending. And finally watch out for opposition when going into the pawn ending. 

why doesn't black take the rook on g1 with check after e7?

OH, i think i get it! through this analasis it seems that if he had promoted it differently the outcome was more or less likely a draw?

Because it loses without any chance after destroying the mating threats on h-file and the possibility of a stalemate trap.

I think there's a slight mistake in your problem. The first promotion should have been a queen, otherwise 4...Rh7+ makes no sense, since 5. Rxh7 isn't stalemate.

Sunshiny, click solution and move list.

I see. So the problem is faulty since 5. Rxh7 wins for white.

Nevermind. It leads to the same ending as the queen.

Yeah if he promotes to queen it will be stalemate.

Good puzzle. What if black tried for the a-pawn?

Nevermind again. I can see black can't reach it.

Good puzzle. 

ridiculous puzzle, this must be fabricated, as if anyone would play any of these moves

Maybe it is, but the logic behind the moves is sound.

Of course this is a composed study (endgame problem) and not a game position. And a brilliant one as well. 

5. Rxh7?? is a draw. 

The underpromotions are the only way to victory for white.

Wait, doesn't black make a mistake by not taking the bishop? 5...Rxh6, and black can draw.