So, a bit of an anlysis.
Joker's gameplay is VERY Fox McCloud. He's a character who you're best bet is to stay away and chip damage with Gun. He has a lot of tools for getting in and out which makes him obscenely tricky to counter. His Gun move in particular has a forward, back, and up dodge that grants slight invincibility AND is VERY fast. Great mix up. His Side B, which I'm not going to try to spell, is a perfect combi tool as well. Pulled off a f-tilt? Side special. Instant chip damage OT. Up B is a pretty good anti air. It has utility but it's very circumstantial. Tether is good though, long reach. His down Special is... bad. Like, it's utility in competitive play is going to be bare minimum. It's basically a counter attack but this counter is substantially more important to Joker than any other characters counter. It's one of the best ways to build up his Rebellion Meter and the Persona is about the only way you're going to get a KO. And that's IF they don't camp you out or out run you to drain your meter. Luckily, all specials are greatly improved with Persona. Gun can gimp much easier and rack up a helk of a lot of damage in no time. His aerials can now be kill moves kuch easier, they're still not amazing but they're decent, his Smash attacks are ludicrous and are still fast, and his tilts are super useful for pressure.
As much as I hate to say it... I think Joker is going to sit right around mid-low. Not awful, and his speed is a BIG boon, but as of now all I can tell is that he depends on the Persona and that thing is not easy to gain. I hope to see people prove me wrong. He's so much damn fun and I'd love to see him in Tournaments but... I dunno. He doesn't seem any higher than mid tier...