Mocks are GunPla drones controlled by AI (Artificial Intelligence) that was first seen in Gundam Build Fighter's final episode, fought against Iori and friends through the final battle. These model kits were specially made by the organizers of the GBWC (GunPla Battle World Cup) to put some spice in the battle.
These models also have different variations of heads that imitates some Gundam and Mobile Suit from different Gundam series.
Here are some of their variations...
Mock also symbolizes the bootlegged GunPlas as in "imitated model kits by other brands"
Bandai has set up this scene to tell the viewers to support the legitimate products.
[ Mock Build Strike Gundam and Mock Zaku ]
[ Mock Jenice ]
[ Mock Satan Gundam ]
[ Mock Turn A ]