Super Mario World/Glitches

Wiggler glitch
The Wiggler glitch allows you to accumulate lots of 1-ups and points and potentially max out the counter.

To perform this glitch, you must go into Forest of Illusion 1 with a cape. Go forward until the wooden platform with the three Wigglers. Now, bounce off them repeatedly. While they will turn red and get all angry, if you leave the screen and come back they will be all calm again and you can continue stomping on them. You will get points, then 1-ups, then coins and afterwards the game will glitch and you will get huge amounts of coins, 1-ups and points. If you do this long enough you will eventually reach 99 lives and a score of 9,999,990.