Flow
From Bulbapedia, the community-driven Pokémon encyclopedia.
Flow is a property that is determined by the weaknesses and resistances of the types of Pokémon inside of the Purification Chamber.
Any Pokémon's type that weakens one of the next Pokémon's types (clockwise around) will cause there to be high flow, while one that does normal damage will be weaker flow, one that is resisted will be weaker still, and one with no effect will be the weakest. For the purposes of the Purification Chamber, it is assumed that the Normal-type is weak to itself.
Flow is one of the most important things about the organization of Pokémon inside of the chambers. If there is high flow among the Pokémon in a group of four, the tempo will raise, causing the Shadow Pokémon in the middle will be purified very quickly, while a low flow will be similar to just walking around with the Pokémon in the party.
Having a high flow (and coincidentally a high tempo) among all nine of the chambers in the Purification Chamber is the only way to purify Shadow Lugia.
