These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Anti-Climax Boss: Okay, Masa is goddamn overpowered, as well as the "Seeded Out" characters, but what's the deal with Yunan? Not only she's more of a middle-tier girl, she's also hard to master for being an unlockable? ...yeah.
Game Breaker: Sean... Well. Sean is the king of this. He looks like a relatively badass old man... at first. After your first match, you'd actually think he's so badass he's way too effective to be in the regualr character roster. He doesn't even have the challenger status which is given to mid-bosses! First, his whip move which is an instant projectile, which he can chain to ultra cheap levels. Then comes his brand air grapple. Then comes his aura attack, which works good on BOTH ground and air. Oh, and these are not supers yet! While his regular moves bring your cosplayer to the grave, his supers bring you to hell. Sean's wave attack, unlike a lot of beam attacks, has a considerably higher hitbox, so without Double Jump, it's undodgeable. But his black hole makes him a COMPLETEGame Breaker: it's unblockable (yet dodgeable, so, naturally, he's a noob basher as well) and it appears right in the place where the opponent stands. Add the fact that EVERY his move throws you back as soon as you're hit, which makes grabbing, shoryukenning or even trying to lunch the lazer beam A LOT harder and you get a definite candidate for a tournament ban.
You're still in doubt? Then count how many continues you spend on fighting him for the first time ever, without playing as Alpha or Zenka. Or one of the challengers.
Goddamn Bats: Pac-Helos are probably the most annoying of the minor mooks because of their electricity attack that prevents the player from melee attacking them without taking damage. Out of the mid-level mooks, Asura is easily the most annoying due to severe spamming of the Hurricane Kick.
Ziro's sound clips are usually taken straight from Hikaru Midorikawa as Heero. But sometimes, when he loses and his self-destruct attempt FAILED, he'll curl down like a crybaby, sucks his thumb and screams "MAMAAAAAAAAA!!!!" in the most high-pitched annoying way possible (thankfully, not using any voices from Hikaru Midorikawa).
Asura's voice clips can get pretty annoying due his constant spamming of specials.
SNK Boss: Zenka, Zenka, Zenka. How do you beat someone who's attacks span all of your side of the screen?
You know a boss is hopelessly broken when the only non-broken moves she has (including normal attacks) is a projectile attack and an unblockable slash attack that reaches across the entire screen, simply because there's a slight delay before it's used. Oh, and her MAX has the same range as her other attacks, is unblockable, and does 60-70% damage.
And then there's Shin-Z, who has 4x the health of a normal character, spams projectiles like there's no tomorrow, and can use the Shun Goku Satsu. Oh, and unless you somehow get lucky and hit him immediately after he attacks, the only time you can hit him is after he depletes his super meter and keeps trying to use his supers anyway (which is more of a weakness with every AI-controlled character, instead of being exclusive to him.)
ALPHA. A 5-level super meter, a projectile that hits everything in front of him, even when the player is up in the air (though there are safe spots directly in front of him and all the way on the other side of the screen,) an unblockable ground pound attack with almost no recovery time, supers with ridiculous damage, and TWO MA Xs, one hitting instantly (and hitting everything in front of him just like Zenka's, though it's at least blockable) and hitting for up to 60% damage, and one that hits for 50% damage, is unblockable, and literally hits everywhere at once (only being knocked down on the ground or in the middle of a teleport can save you.) Oh, and he has Gil's Resurrection ability, meaning that as long as he has at least one level on his super meter, he can come back at full health if he's KO'ed. And unlike the original Resurrection, where you could simply stand in front of Gil's body and jab repeatedly to interrupt it, Alpha's Resurrection pushes the player away to keep that from happening. Needless to say, he puts the other SNK Bosses in this game to shame.
How bad is Another Battle Royale? Well, the first stage is pretty much just a rehash of the 3rd Battle Royale stage, but starting stage two all the mooks are replaced with normal characters, and spawn very quickly. So starting stage 2 you're guaranteed to get stuck in a nigh impossible 4-on-2 match. And then Stage 3 swaps out two of those normal characters with two mini-bosses, making an already nigh-impossible fight even harder. And then Stage 4 decides to pull out all the stops and replace all the characters with mid-bosses (including Beefcake Astro Boy and Totoro) and make the final two characters final bosses. How bad is this? Well, read Shin-Z, Zenka and Alpha's SNK Boss entries. Now imagine having to fight two of them at once, along with whatever other enemies you probably haven't killed yet. Yeah, you might as well just quit.