|This wasn't very hard at all. The enemies all have very predictable patterns, and basically every enemy you can kill by jumping on them. You can also throw apples to stun enemies but it's usually not needed.|
There are lots of gems and other stuff to collect throughout the stages, usually in somewhat hard to reach areas... for every 100 gems you collect, you gain an extra heart container. Green gems are worth 1 and red gems are worth 3. Red gems are also a special limited collectable and the game counts up how many of them you got after each chapter, so for a 100% completion you could challenge yourself to collect every single red gem.
Also each stage has a hidden gold scarab in it, and if you collect it, you get to spin a bonus wheel at the end that can reward you with lives, health, or extra credits (I don't know what happens if you land on the genie face, but the guide says it can vary between a heart refill or a 3up or whatever)... I always got an extra credit whenever I did this. credits are technically better than lives. As long as you have extra credits, the only punishment for a game over is your gem count goes back to 0, your apples go back to 10 (not that those are very useful anyway), and you lose your gliding cloth and have to find a new one.
That last boss (Jafar in his snake form) would've been very hard if I had got game over and lost my gliding cloth...
I ended the game with 49 red games (out of I'm guessing... 70?)