Look guys, Bowser Jr. is certainly a bad character, but that doesn't mean you're allowed to spread misinformation about him.
Smashes? All of them are very impractical.
If you consider a Forward Smash that is massively disjointed even beyond it's animation, active forever, ridiculously powerful, and completely safe on shield to be "impractical," then sure. I mean, oftentimes I exploit how little people know about my character by throwing out random Forward Smashes to make people approach thinking they can punish it only to punish their approach instead. This move is stupid good, and imo one of the best Forward Smashes in the entire game. Beyond this, his Up-Smash is frame 7 grounded* and deceptively powerful, serving as an OOS option, (admittedly his only decent one,) and as a landing trap/mixup. Only his Down Smash is in any way impractical.
Projectiles? One sucks, the other is pretty situational [although important for the character].
"Important for the character" is an understatement, it's integral to a lot of his matchups. The additional pressure created by Mechakoopa makes a lot of his approaches harder to punish, as there are times where if the opponent drops shield to punish, Mechakoopa will walk into them and potentially set up a combo for Jr. The move also makes it really difficult to recover directly below the ledge because Jr. can deploy one directly down, (which helps a lot in the Cloud MU by the way,) and Bowser Jr. can pick it up himself to use as a Link Bomb. Speaking of which, if Bowser Jr. picks up Mechakoopa, Z-Drops it, then picks it up again in midair, the mechakoopa will no longer damage Jr. when it blows up in his hand, which allows it to work as a pseudo-oos option because the Mechakoopa timer still counts down while he's shielding. Finally, trying to pick up grouded mechakoopa is possible but risky for opponent's because of the size of its grouded hitbix, (similar to R.O.B.'s gyro,) and reflecting a grounded Mechakoopa does not grant stage control to the opponet because Jr. can completely armor through it with Side-B.
Dealing with pressure? A big hitbox and the only decent OoS option is the very risky upB out of shield.
Again, he has a frame 7 grounded* Up-Smash that kills around 120%, (depending on rage and weight of course, ) as well as recaught Mechakoopa explosion. Those are his only good oos options though, up-b oos is crap and I wouldn't even call it decent.
Approach options? Nothing is safe on block unless you have a Mecha Koopa in play, sideB is vulnerable and his aerials don't help him much.
His aerials help him out dramatically because both fair and bair autocancel from a short hop, while fair is active forever and disjointed and bair can sweetspot taller chars like Ryu and Rosa from a short hop, making it safe on shield. Side-B is very fast and can be jump canceled, so oftentimes it can be used to get just out of the opponent's range and tomohawk to judge their reaction to the move while simultaneously closing the gap. How they react to it is crucial because the move has mixup potential on shield, and if you respond correctly to the opponent you just got a free approach and potentially converted it into advantage. Plus, on hit, Bowser Jr. has a kill confirm on the entire cast from around 90-110% depending on a lot of factors, so if you don't respect that move, it may cost you your stock.
He basically has all of the inherent weaknesses of a super-heavyheight without the strengths to make up for them. Or actually being a super-heavyweight for that matter.
He has a weight value of 108 and a damage reduction multiplier on his kart, and since damage is a direct factor in the knockback formula, any attacks to the body of his kart do knockback equivalent to being a super-heavyweight, (however, attacks to his body have a percent increase, so if he gets hit in the body he can die like a midweight, which is quite annoying.) He also has superior aerial mobility to all the super heavies, side-b as a mobility tool, disjoints on literally every move in his kit, superior juggle game to most heavies, and on top of all this, relatively high kill power.
Seriously, if you're going to make an informed post on a low tier, please get your information right.
* EDIT: Ironically, I'm guilty of a little misinformation myself here. I initially stated his Up-Smash to be frame 9, but actually it has a launcher hitbox on grounded opponents that begins on frame 7 and ends on frame 9 that launches into the aerial hitbox, while the aerial hitbox itself begins on frame 10. This means that it's 1 frame worse as an anti-air than I initially claimed, but 2 frames better as an oos option. My apologies.