Starred Enemies

I have absolutely no idea what these enemies are for. Are they just normal enemies or do they have some special purpose?
I've seen these kind of enemies a lot and I'd like to know what they're for.
Here's a screenshot https://imgur.com/a/L2p7akI (had to put it on imgur because it wouldn't upload here).

 

That means they're grind mobs. They're much stronger, and they respawn faster, but they drop tons of xp.