The Under Subway (Japanese: ダークライナーDark Liner) runs from The Under to the Shadow PKMN Lab. It was once used by miners before Cipher revamped it to transport Shadow Pokémon. The only way to access it is to go down the stairs from the TV studio, or the Under Colosseum. Inside are rooms where winners of the Under Colosseum challenges may stay in order to receive a promised Shadow Pokémon from Venus. Past the hallways is a system of staircases, that travel down to the bottom to access The Under Subway. In order to protect the station, security has been tightened with Trainers, each possessing their own Shadow Pokémon, all of whom work for Venus. The Subway can also be accessed easily in an elevator which passes the whole system of staircases.
The train that runs on it, the Shadow Liner, is filled with cages to transport Ein's living experiments from the Lab and to The Under. Wes and Rui tried to enter the Shadow PKMN Lab via The Under Subway, only to have their path destroyed by a couple of Ein's minions.
It is unclear where it was originally sent to, as the Shadow PKMN Lab is in the middle of the desert, and there was nothing there before it.
Trainers with a Poké Ball by their names may be challenged for a rematch after defeating certain bosses. In a rematch they may have higher-level Pokémon, and any Shadow Pokémon previously caught will be replaced.
Upon talking to Rider Nelis after battle, her name is misspelled as "Nelia".