Bibby
All right - I'm liking the direction this is going. I don't think I've ever seen an engine that explains this clearly what each command actually does. This would've been extremely useful to me when I was starting out in GM.
The main glitch I see is Mario keeps walking in place if you hold Left and Right at the same time. Changing directions is a bit crude as well, as you keep moving at the same speed when you turn around, and there's no "slipping" animation. And jumping out of the water is awkward, since you don't get much height on your jump.
Lastly, even though this engine is designed to be an example, I'd change everything so the default game speed is 60 FPS rather than the jerkier 30.
Also, I saw a couple of typos: "if only all engines where like this" in the game information, and "automatically" is misspelled in Mario's collision event with obj_solid.
Thanks, I'm trying hard to not forget to explain stuff. I'm really not so used to do that...
As for the walking speed and slipping, working on it. The holding left and right at the same time glitch is fixed, and you also get more height when jumping out of the water now. I'll see if I'll change the FPS...
Lastly, I've added a goomba and some awesome Fire Flower powerups. This engine is also going to contain 3 blank item slots in the game code (powerups that the user can define, default are some black squares)