I have seen Nighthaunts’ Spirit Hosts from Warhammer Age of Sigmar being used in a this way multiple times and it is always impactful. They are a great way to turn a 28mm miniature into a tiny diorama that tells a story.
In this one, Reddit user Rall82 is capturing the moment where the spirit of Rubric Marines from 40,000 is leaving their armor shell after being destroyed.
The last nice part is that you can use the models both as 40,000 models as Chaos Spawns or as Age of Sigmar Nighthaunts!