Merudo
Level: Roachling
Rank Points: 10
Registered: 12-27-2013
IP: Logged

Early on, Regin gives the quest to kill Fafnir.

I completed the quest (spoiler: I killed Fafnir once he transformed into Fenrir in the gemstone mine), however when I go talk to Regin he doesn't realize I killed Fafnir and won't vouch for me!

Moreover, if I bring him back the magic chest he just tells me I stole it from him (as if I pick-pocketed it from him) and he gives me no reward.

Aquillion
Level: Roachling
Rank Points: 10
Registered: 01-12-2014
IP: Logged

This is probably because you stole the reward for the quest from him earlier; the game checks that he doesn't have it anymore, and assumes it's because he already gave it to you.