Skipping the Elite Four (Generation II)
This glitch requires a ????? (hex:FF) first, which can be gotten after receiving a bad clone from the Celebi glitch and taking it into Day-Care and out again. This glitch takes advantage of Pokémon Centers not healing ????? or anything below it; this applies even if you get whited out, so if you lose a battle with ????? at the top of the party, your Pokémon will still be fainted when you return to the last Pokémon Center and you won't get whited out again.
When you battle with no usable Pokémon to begin with in Generation II, this immediately ends the battle (before starting if you have no Pokémon and just before sending out a Pokémon with all fainted Pokémon). Since there are all fainted Pokémon, you can skip as many battles as you want until you switch back ????? to the bottom of the party, or withdraw or receive another Pokémon which can battle.