There is a WQ in Stormheim, Beasts of Burden, where you need to defeat Andurs and Rydyr. As long as you don't complete both objectives, you can farm one fight and get XP. With Lesser Pet Treat, Pet Treat and Safari Hat, I'm getting ~4800 XP at 23-24 level and ~7000 at 14 (this is lowest pet I had). I'm using Rydyr fight for this purpose. I'm assuming it is the same with Andurs.
I am using following team and tactics for Rydyr:
1: carry pet (enough HP to survive first hit, I think 5 level is minimum)
2: Iron Starlette [Wind up, whatever, Supercharge]
3: Iron Starlette [same as above]
- carry pet> pass
- Iron Starlette> Wind up >Supercharge >Wind up (if it does not crit, swap to next Iron Starlette and repeat)
I haven't had any luck with using Toxic Smoke. Two Wind ups with Supercharge seem best tactic so far.