Taffy is not exactly a normal Vaporeon (As evident by the mouth on the end of their tail). The Fae Realm is a Dream-like world oversaturated with unrestrained Life and magical energy. Sometimes without rhyme or reason, that energy and magic decides it wants to be something with thoughts and form, and so it becomes a living pokemon but with some sort of oddity that is not common among their species. Most Fae beings come into existance this way, though there are other ways they can be made as well; They can also be birthed from normal pokemon or a normal pokemon could be turned into a Fae pokemon through overexposure to the energy of Fae Realm such as eating Food of the Fae Realm, which famously binds mortals to to the realm and typically includes too way much sugar, the Fae do not understand restraint.
Note: Not all Fae Pokemon are Fairy Types and not all Fairy Types are Fae Pokemon. The Fairy Type uses the Life and Magical Energy of the Fae Realm, just as not all Ghost Types are literal Ghost but have Ghostly powers that come from the Fae Realm's mirror opposite, the Spirit Realm.

Taffy is very sociable, they love being around other pokemon, they like being involved in whatever is going on, are very high energy, and likes to be helpful, but they are also naive, they don't understand privacy or personal space, and take people's words a little too literally. Be careful around their tail, it almost has a mind of it's on and likes to bite things out of curiosity or boredom.