Ν | Pokémon Heartgold/Soulsilver Tweaking Glitch - Hidden NPCs in National Park @N_i_ | Uploaded November 2010 | Updated October 2024, 3 hours ago.
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I haven't confirmed this, but that NPCs are the same who appears after you win the Bug-Catching Contest. If there is a beta NPC there, I don't know. Bug-Catching Contest is so tedious... ._.