I've mained AP Shaco up to my 370k mastery points (probably another 200k b4 mastery system was put in the game)
Playing AP Shaco is a completly new experience, it takes alot more skill to play AP Shaco than AD Shaco, because you have to carefully plan your actions AND the actions of your enemies, every single of your abilities are useful, whereas half of AD Shaco's abilities are just useless (his ultimate deals 0 damage, his boxes are only useful to run away from a fight).
While playing AP Shaco, you're not just autoattacking your enemies to death, you actually HAVE to find ways to outplay your enemies by making up a strategy, instead of having the game babysit you with tons of passives such as Ekko's or Yasuo's passive. You make a mistake, and you're most likely dead unless you're already fed. That's what makes it so fun to play AP Shaco, even though it's not ''the best pick'' in most situations since, as i said, the game doesn't babysit your ass, it feels extremely rewarding when you outplay them, and people will recognize your skill (I've had so many people typing in all chat about how they got outplayed and how good i was at playing Shaco)
There's also a good chance that Shaco's going to get a rework/update soon, so learning how to play him in different ways could prove benificial if he becomes stronger than he already is.