I've been looking for months for this game, and I think reddit is my last option here! I was a child when I played this game on the school's computer, but i can remember it really well. Here are the main caracteristics of the game:

-It was released before 2007-2006, probably before this. Charlie the Duck (1996) was also installed on the pc

-It was a 2d plateform game

-You character was a blue little dragon that could only walk, jump, and could attack but i don't remeber how

-The goal was to climb a tower. Each level was a floor and yo had to reach the exit by jumping on the plateforms

-The main ennemies were green bubles comming from green water pools -You could only take one hit before dying

-There were some boss, although i never reached one

-the school had the demo version, you could buy the full version if you wanted too.

That's all i can remember , i'll try to post some picture that look like the game. Thanks for your help!