If Cobalion, Virizion and Terrakion are allowed on the Battle Subway/Random Matchup, why isn't Keldeo?

Question

Keldeo has exactly the same stats as the other members of the Musketeer Quartet, and a stat total of 580. All the other legendaries with that total are allowed. Is this because it's an event Pokemon?

Answer 1

Yes. All event Pokemon are banned from the Battle Subway.