<Snipped quote by Adorabadass>
Darkspawn tainted Mabari found wandering in the Deep Roads perhaps? Might be useful to have a Grey Warden hound who can sense Darkspawn coming by your side. It'd be a little mean towards Martin and Karras though, so best keep it on a short leash.
Actually Mangy could at some point accidentally consume the blood of darkspawn and end up as a gray warden hound.
I have a headcanon that Mangy is the second smartest party member(Etta's got claims on that title) so having him sense darkspawn and warn others of danger would be right up his ally.
Could actually have him start barking at grey wardens if they get too close to Martin or Karras because Mangy cares about his allies.