This technique, involving an old man glitch glitch Trainer was documented by Paco81.
RequirementsAny old man glitch name character (name position slot 3, 5, 7 or 9) corresponding with a Trainer. See The Big HEX List. A very strong Pokémon, preferably a Level 100 one with several X Speeds and at least one X Accuracy to secure a one-hit KO on six Level 250 Pokémon with Horn Drill, Fissure or Guillotine. Tauros is a good choice.
Steps1. Battle the Rocket on Silph Co. 11F
2. Fly to Viridian City and perform the old man glitch (trade link up shore encounter glitch might also work if the player doesn't have the required name, but this is unconfirmed)
3. Battle any glitch Trainer from the left-facing shore tile, until they send out a "94". Afterwards, your fourth item may have changed.