A neckerchief OR a collar and half a leash OR your favourite ball
1 Sleight of Hand
1 Tunnel Fighting
1 Bite Fighting
Decide if you are, in addition to being a good dog, a big dog or a small dog. Big dogs get +1 Bite Fighting and +1 Dig, small dogs get +1 Tunnel Fighting and +1 Awareness.
May only carry half the normal number of items. Has all predictable dog related limitations, like not being able to wield a sword. May however cast magic is you find someone that can teach dogs to do it. Good luck with that.
Playing a totally mundane dog in Troika! would be very appropriate. Not everyone has to be a show stealing attention hog, some of us just want to be loved and rescue people from wells. They're emotive creatures as demonstrated by the players usage of body language while playing them:
I growl in a way that says "there's a goblin hiding in that tree drawing pictures of us while we eat"
I stare at them in the manner of someone who wants to buy that magic necklace and get it fitted to dog sizes. Use the money in my satchel.
The Good Dog has more baked in potential than all your lamassus or floating-head-conglomerates combined. You have to work to make those as fun.