Underground Ruins — Pokémon Black 2 & White 2
Every wild Pokémon here, by encounter method.
Underground Ruins lists 11 Pokémon across 4 encounter methods (grass, dust cloud, static encounter (with the ice key), static encounter (with the iron key)), between level 54 and 65. 3 of them are on no other route's wild tables in this guide: Regirock, Regice, Registeel.