Odds are you’ll have a favorite early. Pick a beast of some kind, or any pet with a Critter power ability. Once you get out to Valley of the Four Winds have your high level critter killer in slot two and whatever low level in one. Circle Halfhill and attack everything. The Bandicoons are critters and rarely will you run across an Otter, which is Aqua.
Get the first attack with the low level and switch it out for the rest of the fight. Easy XP.