PK5: Uncatchable Legendary Beasts

In Pokémon Black and White, when players bring one of the Fateful Encounter Legendary Beasts to the Lostlorn Forest, an in-game event activates.

In the in-game event, you'll be approached by a camper, who would then growl and start a Pokémon battle.

The Pokémon battle starts with a Raikou/Entei/Suicune, but upon one hit it would be revealed that it was a Zoroark disguised using its Illusion ability.

As it turns out, the Raikou/Entei/Suicune at the start of the battle actually contains fully populated Pokémon data, that was obtained via a RAM dump.
These 'legendaries' are normally shiny locked.
 

Credits: @Poke J

Source: https://projectpokemon.org/home/forums/topic/39815-unreleased-prototype-pokemon/?do=findComment&comment=268584