Node wizard Simon Thommes has written an extensive post on the Blender Studio blog detailing the denoising process for Sprite Fright. This in-depth look contains a treasure trove of information on the problems, thought-processes, and solutions put in place by Simon and the Blender Studio team to render Sprite Fright silky smooth and noise-free.
— Blender Studio (@Blender_Cloud) November 26, 2021
The main challenge Simon outlines in his article are already-denoised final shots that still had flickering and noise problems, and how to creatively mitigate this type of noise in Sprite Fright's use case. The issue is with noise on animated shots: while Intel's Open Image Denoiser does a great job on still frames, it lacks temporal stability. The method they ended up going with was using Geometry Nodes to dynamically generate a Z-depth-based recreation of the background, on which a single noise-free render is re-projected.
Check out the article on the link below for a really in-depth explanation of the process, and a ton of videos and images showcasing it in action!