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According to _Dragon and Drakero this is the spot for both Blacephalon (and Stakataka):Hi:
I am attempting to RNG Blacephalon in Ultra Sun. What is the exact location I must stand in while in Poni Grove such that I have 0 NPC's affecting my frame advancement? In the RNG tool, it automatically lists 0 in the # of NPC's box on the right with a correction of 9. Where exactly do I stand so that this is the case? Also, is this RNG done by using a Honey Pot to trigger the encounter?
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