Filters>Animation>Playback?
My old "progressive-merge.py" will generate all the layers produced by progressively increasing the opacity of a top layer over a bottom layer.
Since it supports layer modes (2.8 style) you can put the top layer in Dissolve mode:
My old "progressive-merge.py" will generate all the layers produced by progressively increasing the opacity of a top layer over a bottom layer.
Since it supports layer modes (2.8 style) you can put the top layer in Dissolve mode: