Tricks developers use in platformer games.

Links for some more in-depth explanations:

http://kpulv.com/123/Platforming_Ledg...
http://kpulv.com/106/Jump_Input_Buffe...

Good discussion on gravity in games:   / do_most_3d_platformers_use_the_same_gravit...  

Crumpled paper from vecteezy.com