The Great Cave Offensive is a new stage in Super Smash Bros. for Wii U. It is a very large stage based on the underground labyrinth gamemode (of the same title) from Kirby Super Star.
This is a very big stage that has multiple sections that appeared in the gamemode. There are Danger Zones that give massive damage, and if someone touches one them at 100% or higher, they will be instantly K.O.'ed. There are also spikes in some areas. It's possible to ride in mine carts that randomly appear; if you run into someone else while riding said minecarts, they will take damage. In the lower parts of the level, there are cannons that can launch other players. Sometimes, Treasure Chests will appear. Hitting one will drop an item.