In Vs. Marowak, Cobalt used Marowak's Rock Smash to destroy boulders in search for a fossil. When Ian and Elise find them, Cobalt has Marowak attack them. It attacks at Elise, with Ian's Sandslash defending her. However, this left Sandslash open to attack, and is defeated by a Double Edge. This revealed its Rock Head ability. Marowak continued to target Elise, her using her Horsea to try and stop it. Ian then chooses Charmeleon, it landing a blow. However, Marowak overpowers it and defeats it. Horsea uses a Smokescreen to hide them, as Cobalt and Marowak continue their search. The find a Dome Fossil, and make their escape shortly after that.
In Vs. Silver 1, it is revealed that Marowak was Cobalt's first Pokémon, obtaining it as a Cubone. Cobalt trained it to beat his brother Silver's Cubone, which it did.
In a flashback, Cobalt chooses Marowak to battle Silver's Marowak before escaping. Cobalt's Marowak wins with ease.
In Vs. Clefairy, Marowak appeared in a flashback as a Cubone, battling against Silver's Cubone. Cobalt's Cubone was clearly stronger and defeated Silver's with ease. In Vs. Sudowoodo, this flashback scene is shown again.
In Vs. Marowak and Roselia, Marowak teamed up with Domino's Roselia to battle Silver's Abomasnow and Dawn's Cherrim. Marowak overpowered and defeated Abomasnow easily while Roselia defeated Cherrim. It battled Silver's Gengar next, as she had countered Toxic Spikes. Marowak defeats Gengar quickly. It then battled Silver's Marowak, the two having been rivals forever. Cobalt's Marowak holds the Thick Club to take the advantage. Silver's Marowak uses a combo using a cotton shield, and Cobalt's Marowak is eventually defeated.