Tunnel/Door that removes collisions and textures inside it. Probably needs to be scaleable like cubes and such to help fit through different thicknesses and spaces.
Back when I made maps for Battle Front II(original), the best items were the ones made to clip through terrain without you having to sculpt or clip open the ground. So you could drop a tunnel into the side of a mountain and walk right through it under the map.
I havent done any map modding since those days so idk how common of a tool this is in modern engines. But it feels like it would be a damn neat item for condo building. Place a door literally anywhere in the condo regardless of where walls are in the way. A lot of people like to build outside their condo's limits by clipping through the ceilings so this would just add a more legitimate way to 'break the game'.