On Borrowed Time: Chapter 6, Page 31-32 (Patreon)

skuntank's aura is green because he's smelly and rude

also, a big stroke of luck for me that skuntank and vulpix are both in the same IQ group! in another draft where rune was learning this from a different character, the other character's species actually didn't have the stair sensor skill

Edit: Released for Normal Rank+!