Planet Wisp Act 1 2D-in-3D glitch [Sonic Colours Ultimate]
Near the end of the act, use the spike to go all the way left, then collect the jade ghost to take the upper path. Go right and you will see a spike wisp, collect that and go over the barrier wall [Wall-less (for a lack of a better word)] and go all the way left. However, as soon as you go diagonal, jump. You will be in the drift section with 2D movement.
The next thing to do is to use the “collect a 2nd wisp (rocket) while in wisp form” mechanic to your advantage. Carry rocket while in spike form all the way through, then use rocket in the drift section.
Btw, I was bored and messed around, then stumbled upon this. This was recorded on my Xbox Series S.