A Form can be changed in Geometry Dash by travelling through various portals. For each form the player can assume, the method of control differs slightly.
List of forms Edit
Cube: The cube is the standard mode. Tapping makes the cube jump three times its height, while holding makes the cube jump in succession. It must be touching a surface in order to perform actions, but will crash if it collides with a physical object either above (or below, under the effects of antigravity) or in the direction it's moving, and will be destroyed if it hits any hazards such as spikes and saw blades. Its controls appear to be based off of the player in The Impossible Game, and the whole game is generally compared to it due to this being the most used form.
Ship: First found in Stereo Madness, the ship abides by gravity, but is propelled continuously upwards (or downwards, under the effects of anti-gravity) by holding. Not touching the screen will result in descent. It can safely make contact with physical objects above and below it. Its controls seem to resemble mobile games Iron Pants or Jetpack Joyride which have very similar controls.
Ball: First found in Cycles, the ball is controlled strictly by directional gravity, and will travel vertical in either direction when tapped, as long as it is in contact with a surface. Tapping while over a jump ring is the only instance the ball maintains its current gravitational path after jumping, while tapping while over a gravity circle will allow a midair change of gravity. Holding will only shift the gravity once and subsequently does nothing. It can safely make contact with physical objects above and below it. This form also resembles Gravity Guy, a popular game available on mobile devices.
UFO: First found in Theory of Everything, the UFO can only perform small vertical hops by tapping, abiding by gravity. Holding will not result in any action other than the first tap. It can safely make contact with physical objects above and below it. This form was supposedly inspired by the mobile hit, Flappy Bird, which featured very similar gameplay.
Wave: The triangular object moves diagonally at all times in either an upward (when player holds screen) or downward direction. It cannot make any contact with physical objects, except for the ground or ceiling. Tapping while over a jump ring does not contribute to its movement but gravity rings, pads or portals will affect its mechanic (tap to go down and release to go up!) First time used in Blast Processing. When the wave is in its shrunken state, it moves in a steeper angle and therefore seems harder, first encountered in Theory of Everything 2. This form was likely inspired by the game Wave Wave, which features both similar gameplay and icon.
Robot: First introduced in the unreleased update 2.0, this vehicle walks on two legs and has the ability to jump higher than the regular cube. It is said to resemble the "Lil' Stomper" vehicle from the mobile game Jetpack Joyride. It appears, as shown in the closing seconds of the second Update 2.0 sneek peek, that its jet boots give it a controllable jump height, and that its primary color sections are the head and legs and that its secondary color sections are the eyes and jaw.
- The gravity ball might be a reference to the flash game called Gravity Guy, which uses the same mechanics as the gravity ball. Other possibilities are one of the game modes in the mobile game, Jetpack Joyride, and the gameplay in the game VVVVVV, which uses a similar mechanics as the Gravity Ball.
- The UFO is modeled after the "flying saucer", the most common representation of alien aircraft.
- The wave form is inspired by the mobile game Wave Wave.
- The wave was also the only form to use only one icon when it was introduced in Update 1.9. The Update 2.0 teaser shows two more wave icons, although they cannot be unlocked to date as the update has not been released, and as such only the default is available.
- There is one UFO icon (30 Map Packs complete) that references Bowser Jr's clown car from the Super Mario franchise.
- There is one cube icon (Hexagon Force complete) that references a Creeper face from Minecraft.
- There is a glitch where if the ship is upside down and the ghost trail is on, the icon reflections will be right-side up.
- The 'Steamrolling!' icon (First 3 levels complete, unlock able only in the Steam version) may not be inspired by, but looks very similar like the companion cube from the Portal franchise.
- The wave's trail follows the beat of the music.
- Oddly, if you use the rainbow tail, it will be hidden behind the wave trail.
- The wave currently has no customization options, apart from choosing colours.
Note: The above trivia has been taken from the original Geometry Dash wiki.