If you mean the numbers appearing when you hit a mob, that is most likely ToroHealth Damage Indicators (found here). If it's the mobs collapsing you are after, the only thing I can think of is the Mob Dismemberment mod from Ichun. However, that mod is not 1.16 compatible and therefore it is highly unlikely this was shot in 1.16. Try finding the mods in 1.12.2, I'm sure a lot more useful results will show up.
Thank you for this info! It's close but doesn't have the same flashy style this damage indicator has with the fancy text popping out on critical hits. It's closer than anything I've found while looking though.
There used to be an older mod just called Damage Indicators, that one might've been flashier but definitely isn't for the latest version if anything. Otherwise it was the Neat mod, which performs a similar function. I don't think there are other alternatives.