Marth's Swordsman Spike/Invisible Ceiling Gitch
The swordsman spike and princess spike are glitches in Melee that take advantage of the game confusing counter hitboxes and shieldboxes. Since receiving knockback after hitting an opponents shield can trigger the invisible ceiling glitch, counters exploit that can are easily able to trap opponents into a permanent invisible ceiling, as long as he remains in the air and is on the left side of the stage. Melee is wack, man.