Mario&Luigi is fanmade Mario game
Tricks:
Jump-on detection:
This game seems to use the common jump-on detection algorithm in Mario games: If you are moving downward while hitting some enemy, you jump on it (and don't die unless it is piranha plant or spike top).
Piranha plants:
Piranha plants don't hurt mario while they are popping up from pipe (while going down they do hurt him).
Left+Right:
If you press left+right, Mario instantly changes direction.
Cornerboosting:
If you hit block suitably from below, you go bit inside it and get ejected. This saves 2 frames a pop if performed correctly.
Picking up bonuses inside block:
If you hit block that's ejecting bonus with sufficient speed, you go bit inside block and hit the bonus, picking it up.