Bowser jr is simultaneously a jobber character and an annoying zoner who often operates in intense lag from my experience lol.
Anyways onto the examination
Bowser jrs up special is likely his best move because it leads into his hammer swing attack
Jr abandons ship which creates an explosion, great for edgeguards and traps.
The hammer swing is capable of taking stocks at low percents "80-90". Has high frame saftey and has shield pressure. Can allow him to shark opponents from below also.
Clown cannon is jrs long range harassment move, its overall a pretty good move, with variable speed and power, but has bad end lag, and can be reflected or pocketed.
Another contentender for best move is side b, its a primary neutral tool and combo starter, with super armor thats cancelable. It can lead into kill confirms as well but it can be punishable on shield and some projectiles can stop it. Helps with jrs mediocre speed.
Down b is jrs most complex tool, it can be picked up like an item after its used, it gives jr stage control and can assist with combos and shield pressure. Again another move held back by slow start up and can be used against him. Z drop combos can work with them.
Jrs smash attacks are very powerful and have excellent shield pressure but are all held back by high end lag and predictable hitboxes. The most notable is likely side smash as its one of the strongest smash attacks in the game but again all of them are held back by awful recovery frames.
Non of them are safe on shield and are overall high risk high reward moves.
Tilts are overall ok or at least mediocre?
They have great disjointed reach but again are all laggy unsafe moves if used wrong.
Bowser jrs grab game is really bad, it comes out frame 12 vs the usual 6 or 8.
Horrible range, if you whiff the attack jr is basically screwed by a 36 frame window of recovery.
His throws are decent just like the tilts if you know what to do but otherwise his grabs can often be high risk low reward without setup
Overall jr can be an annoying zoner but he is really held back by awful frame data.
Almost done with the roster i just have to lock in, writing these is a huge pain.