This video outlines a good method to create a pseudo 3D or 2.5D parallax effect in the GODOT 2d game engine. This parallax is different from the one you often see in endless scroller games, and does not use the ParallaxBackground node. Hollow knight implements its parallax using the 3D engine, which has some advantages in regards to lighting. However, the parallax effect will function the same way using this method and it is better for anyone preferring to work in the 2d-engine.

Further reading on the pseudo-3d effect can be seen in Godot docs:

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