An AzerothCore module for horizontal progression through zone-based passive auras. Step into a themed zone and you get a hidden, passive resistance buff (a "biome"), leave it and the next one swaps in or gets removed, automatically.
Each zone belongs to at most one biome. There is Frozen (frost, e.g. Dun Morogh, Winterspring), Volcanic (fire, e.g. Searing Gorge), Toxic (nature, e.g. Swamp of Sorrows) and Arcane (arcane, e.g. Netherstorm). No buff icon, no client patch, not dispellable. Two optional trinkets amplify a biome further and stack with the zone aura. Works for real players and bots alike.