Some 2D games use 3D geometry for the environment and characters, but restrict the gameplay to two dimensions. For example, the camera may show a side-scrolling view, and the player can only move in two dimensions, but the game itself still uses 3D models for the obstacles and a 3D perspective for the camera. For these games, the 3D effect may serve a stylistic rather than functional purpose. This type of game is also sometimes referred to as “2.5D”. Although the gameplay is 2D, you are mostly manipulating 3D models to build the game, so you should start the editor in 3D mode.