Originally posted by Gregomoto:

Not sure if the rested buff effects eitr regen at all. Afaik rested buff has „only“ following effects:
Health regen +50%
Stamina regen +100%
XP gain +50%

Rested definitely effects Etir regen even though it's not listed.

Now what stacks and what doesn't stack is the question.

Honestly I feel like the Robes are highly unnecessary as the Fenrir Gear movement bonus is better when just blowing through low level content with Magic and the Carapace or even Padded Gear is better for defense when fighting Mistlands content, the bonus Regen isn't really necessary especially since you can just use a Stamina weapon while you wait for it to regen and chug Mana Pots if you want.

On top of that, even with just the Rested Bonus once you have decent Elemental Magic you can just Fireball, wait for the dot to fall off, then Fireball again, the Etir amount it costs should regen by the time the dot falls off. (And since the DoT effect can't stack, not much reason to spam fireballs)