All animals (or even just most) is impossible, intelligence is costly and unintelligent ones would quickly outcompete intelligent animals in many niches, even if you just hand waved them intelligent. It also requires specific biology that is incompatible with many forms of life, you can't put a big brain in a snake's head and still have it look or function anything like a snake. Even if your surprise intelligent animal is trying very hard to uplift other animals they will fail most of the time. Worse if they don't realize this they aren't very intelligent. 

So yes you are going to have to hand wave it as magic and basically ignore most of biology with an even bigger hand wave. At that point having to make your created animals intelligent does not make much sense since you are already ignoring all of the relevant biology, they should just BE intelligent for no reason (because fantasy) since that is already true for everything else.