Hobgoblins' eye changes based on whether or not it can use Thermal Barrier. I've killed well over 10,000 Hobgoblins and yet not once noticed this small detail until I was just mucking about with the HUD off.
[spoiler]Left: On cooldown
Right: Active[/spoiler]
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There was a pair of hunter boots available in TBD whose flavor text read that they changed your footprints to mimic different animals so you couldn't be tracked. I spent days on different planets walking around, looking down, dying constantly, and not once did my prints change to an animals. I uninstalled the game and never looked back. I don't have time for that kind of negativity in my life.