As you probably know, Damage Indicators isn't updated to 1.9. Are there any other mods that do the same thing it does I can use in 1.9? It needs to be able to handle mobs with possibly over 1,000 health.
I have released a mod that shows damage indicators for v1.9.4, if that's what you're looking for. Check out ToroHealth Damage Indicators and see if that fills the purpose you need, if you're still looking for that. Not entirely sure how it handles mobs with over 1000 hp, but it should be fine. The hearts display may not work properly, but numeric should.