I got Spiritomb in BDSP. AMA about the process : r/PokemonBDSP

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HOW TO GET SPIRITOMB IN POKEMON BDSP EASY - NPC UNDERGROUND MAP - Brilliant Diamond / Shining Pearl

Guide: How To Find Spiritomb In Pokemon Brilliant Diamond/Shining Pearl – NintendoSoup

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Route 209 Spiritomb - English - Project Pokemon Forums

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Ultra Square Shiny Spiritomb - 6IV + Max Stats Efforts and All Moves for Pokemon Sword, Shield, Brilliant Diamond, Shining Pearl, Legends Arceus, Scarlet, and Violet - elymbmx