As with every game, Geometry Dash contains several glitches that causes strange events to occur during gameplay. This is a non-exhaustive list of glitches in Geometry Dash, particularly those that happen during gameplay.
However, RobTop may fix these glitches if he finds them impractical and not useful.
Cyrillic claims to use some kind of verification glitches to verify his impossible levels like Silent Circles, but is likely false as he has never confirmed anyone what his glitch is. Some levels like Slaughterhouse by IcedCave was verified using Cyrillic's verifying glitch.
Probably one of the most famous glitch, this involves lining consecutive slopes on top of each other with one small step between each other. The result is when a form enters from any point in the slope "tower", it will come out from the top. However, this glitch is redundant due to the teleportation portals being added in 2.0.
Luring a form out of the screen
Create a set of blocks with each subsequent block one small step below the previous until it reaches the bottom of the map. Now make a form travel in antigravity below it. You will notice that instead of crashing when there is insufficient space, the form will seemingly exit the screen and will move back to its place when the line of blocks stops.
This glitch was fixed in 2.01.
This glitch allows one copy in dual mode to be in front of the other. You will need to create two rows of speed portals, one of the orange portals and one of the pink. Now, when the pair of icons passes through these portals for long enough, one will start to move in front of the other.
This glitch was fixed in 2.0.
Copy spawning at the end of level
If a dual activation portal (orange) is put with the flat side facing down and one space away from the ground, and a form is made to move below it, the portal will be triggered when the form completes the level and goes into the finishing line, thus spawning another copy of the form that strangely stays on screen.
Conversely, if the player is in dual mode and a dual deactivation portal (blue) is placed in the same way, the player becomes single mode again, with a "ghost image" (Player 1 colour portion) of the other icon staying on screen.
Spike behaviourIf placed in the right way, several seemingly close spikes can actually let a form slip in between them. It is because of that the spike's hitbox is smaller than the spike itself.
Blue orb glitch when exiting Practice Mode
Infamously used by some users to verify impossible levels, this glitch involves going into practice mode and going very close to a blue orb but not quite activating it. Pause the level, deselect practice mode and tap rapidly. If lucky, the player may end up starting in antigravity due to the blue orb script triggering at the start of the level. Users can then put a portal for a secret way. This was used to verify levels such as Nova Cataclysm.
Objects before the starting line
Put a move trigger at the beginning of the level to move whatever objects you want before the starting line. Do a playtest and pause it. Copy the objects before the starting line and remove the object(s) from the group that moved the original object(s) to before the starting line. Stop the playtest, then and delete the original object(s).
https://www.youtube.com/watch?v=b1w3k5MKyEw (9 Geometry Dash glitches)
https://www.youtube.com/watch?v=AwIrB34FXJY (Objects before the starting line)