PK2: Debug GS Mons .

These Pokémon can be added to the box by the devs for the Japanese debug versions of Pokémon Gold and Silver via the debug menu.
This option was added to the debug menu,  presumably to enable the devs to run through the game and debug various features.

It appears that the OT is randomly generated by pulling from a list of possible names, as well as having fully random TIDs (the TIDs are not tied to the OT).
Additionally, the other details, such as species and DVs are random as well.
At this point, it is not known whether Unown, Larvitar, Pupitar, Tyranitar, Ho-Oh, Lugia and Celebi can be pulled as the random species.
Though it is important to note, with the basis of about a 100 saves, it does not seem possible, as none of them have even appeared in any of them.

It is also not known is it is possible to get a shiny, or the DV is restricted to randomize in a way that it only outputs a non-shiny combination.

Depending on which debug option was chosen, it either places you in Viridian City Pokémon Center or in your house.
It also gives you a Lv 80 final evolution of a Johto starter, and it gives you random Pokémon in the entirety of Box 1.

[We will not distribute the Debug ROMs and SAVs, and it is against our rules to ask for it]