After discussing with Zblader, here's more or less what the conditions on your 'Niddhog' will be.
1. Quintessence eating is out. That's more likly than not going to end up ludicrusly expensive.
Instead, you'll have to just 'send it hunting' for food. If a fight starts up, you can 'call' him, but he'll show up after a few turns.
2. Using 'Niddhog' when you're in a building will limit his abilities- he'll either end up having specific attack spots, like reaching a claw through a window, or lightning blast, or he might have to circle around if the local elementals freak out..
In short, he's awesome, but impractical as a general rule, be prepared to fend for yourself without him.
