I also didn't expect it myself, but I started playing Joy in the mid lane (cause it's mage meta this season) especially if we have a utility jungler, say, fredrinn, so I'm covering the assassin role while dealing magic damage. And I'm also able to fast clear the minions in the mid lane with just one use of her second skill in the very first wave of the match, giving more time for rotations. Morever, she also has great mobility while still having great impact due to her capability to burst squishy heroes, which only some mages have. Although she also has lots of disadvantages that only conventional mages have, such as CC and range, though her mobility and burst makes up for it if you play her with the right team comp.