I can't decide if I like: Merlin always runs warm because of the dragon blood inside of him, or, Merlin always runs cold after the dorocha attack, more. So, if you see me flipping through the two in my fics don't ask questions
But truly I think my favorite idea for Merlin's body temperature is the secret third option of Merlin always runs cold because being a dragon lord makes him cold-blooded so the way he gets warm is through the use of external heat (cue Lancelot and Gwaine always hugging him and cuddling with him and sitting him closest to the fire so they can make sure he is warm enough)












