We have released a plugin for Fusion that allows you to automatically combine a series of frames into one output image. Up to 25 images can be combined in one viewport and arranged as a row, column, or Brady Bunch-style grid pattern. The central frame can be chosen explicitly or set at a relative offset from the current frame.

Footage courtesy openfootage.net

This simple tool is helpful for visualizing the effects of adjusting keyframe values across multiple points in time.