PK1: The "Hooked" Series .

In Pokémon Red & Blue, a strange glitch was discovered by the GlitchCity old forums. (Less loud and more readable version here)
According to the report, it appears that after performing a variant of having the Safari Step counter time out when the boy in Pewter City take the first steps to bring you the the museum, talking to the boy again afterwards will result in a "hooked" Dragonite appearing, before freezing your game.

Jojo12100 was able to dump its info and replicate it, much like the process done for the Gen 1 Ghost Marowak.
Do note that in the data, it's level is 0. (PKHeX views any species with 0 EXP as Lv 1)

Besides Dragonite, other possible "hooked" encounters includes Metapod and Missingno. Those encounter are triggered by different conditions.

This page has an explanation of how Hooked Pokémon glitches work.