Braincrushas are a type of Ork heavy tank. Mounting a massive cannon, the Braincrusha fires gigantic shells at high angles which can decimate enemy tanks.
The Braincrusha cannon fills almost the entire body of the tank so the crew have to squash together in a small tower over the gun's breech, which vibrates with the concussion of the cannon's recoil. The noise and vibrations Ork crew experience while piloting this tank is likely the reason it is called the Braincrusha. Judging from its size, it could be equal in weight to that of the Battlewagon. So in a sense, imagine it as a Battlewagon but with its crew compartment and its assortment of gunz being replaced by a ECKS BAWKS HUEG Fuck Off cannon. That and its front wheels must be absolutely massive, potentially running over smaller and lighter vehicles in the process.
In a sense, the Braincrusha possibly functions as a dedicated long range tank killer more in line with the SPESS MEHREEN Cerberus Heavy Tank Destroyer than it does with more conventional heavy vehicles. Thus, the Braincrusha should function in a similar vein especially when you consider that its giant FUCK OFF cannon could possibly turn a Land Raider inside out in one shot. Furthermore, its tower could actually act as a spotter to allow the gunner to aim and fire. Meaning that ridiculous house on top actually has a use.
It also has the dubious honor of being literally a moving house with guns with a complementary watchtower on top. Also, how it is able to provide a high angle shot with what appears to be a static cannon is up to some serious debate. Due to the scarcity of images of the Braincrusha, let alone models of it due to coming from the old days of yore, the Braincrusha might be the most elusive Ork vehicle to date.