PK thunder freeze glitch
From SmashWiki, the Super Smash Bros. wiki
The PK thunder freeze glitch is a specific glitch for Ness with Fox in Super Smash Bros..Only two players are required for this glitch. Choose a stage with a direct line between Ness and Fox (ideally, Hyrule Castle or Sector Z). PK thunder against Fox's reflector so that the PK thunder is in direct line back to Ness, and quickly bat the PK thunder away. The thunder should have two tails, and if it reaches the edge of the screen, the game can't handle it and will freeze.