You know how to battle a Pet Trainer, right? You just put your lips together, and blow this whistle. You might want to have a fully stocked Battle Leash first though, because Pet Trainers won't stay around waiting to fight you forever!
Pet Trainer Whistle price in Growtopia: sells for about 6 WL, buyers pay about 4 WL (median of 316 offers from community Discords, past 30 days). Live price chart and the latest buy and sell offers.
Recently sold at: GJUAE, YP7S, JAHO, ZRHLP, GUWL