here's a list of y favorite glitches:
1 Super Mario World: powerup incrementation, "zombie" Blue Yoshi, gray Buzy Beetle shell, P-Switch with unlimited uses.
2 Sonic the hedgehog 3 (alone) HidroCity boss music glitch (get out of water when the drowning theme plays).
3 Sonic the hedgehog 1 (genesis), :Getting to the end of Scrap Brain zone act 3 (A.K.A. Labyrinth zone act 4) almost instantly by zipping through wall.
4 super mario bros (NES): minus world (-1) , beyond world 8-4 (only if you place a flagpole by hacking the game)
5 Mega Man 4: "kill" Dr. Wily by using rain flush (acid rain) when he escapes with his escape pod after Wily Machine (fought after the boss rematch) gets destroyed, as result, the level won't be beaten, forcing you to restart