Breeding Marowak with Shieldon produces a Cubone with Swagger

[Former user]

Trying to breed to get a Marowak with an Iron Head, and as the wiki says, this is done through either the Aggron lineup (which, AFAIK, is impossible to obtain in insurgence) and the Shieldon line, so I've been grinding solely through a Marowak and a Shieldon. However, rather than any of the moves one'd normally get through this, I'm getting the move Swagger, which hasn't been shown in both the Insurgence wiki, or for that matter, the Bulbapedia wiki