Regurgitator
 

I turned in the regurgitator to Mammoth in surefall but all I got was
"Mammoth growls" with nothing in return.

Since it requires a trip from surefall to ak'anon to surefall I was hoping to get a GM compensate me as well, I'll try tomorrow in a petition.

The quest has a chance to give you a "bad" regurgitator, that just upsets Mammoth. Its intended.

Yep. Sounds like a bad Regurgitonic.

Is there any way to identify the proper regurg?

If you can cast the Identify spell, which all enchanters should be able to do by level 16, it will reveal whether the tonic is a good mix or bad one. That's still a long dang run from Surefall Glade to Ak'anon to gamble on getting a bad tonic, so I prefer to make a koalindl corpse for myself :D