Out of my entire For Glory experience for the past two years and from what I commonly come across myself:
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Cloud
I'm honestly just sick of seeing him 8/10 times I go onto For Glory. I will enjoy fighting a good Cloud player (and I have come across some that have absolutely bodied me before), but what really peeves me are the ones that run away and Limit Charge the entire match. I hate these Clouds specifically. They rely on Limit Charge far too much and absolutely refuse to fight until it is charged.
Then of course, they roll spam and almost always go for Finishing Touch. They never try to save it, or hardly use the other B moves he has. I've even had Clouds try to use it on me when I'm at 0%, and I honestly have to wonder why one would waste it like that.
Sonic
I'm so glad that I hardly run into Sonic's anymore, but when I do they're always the ones that Spin Dash all over the stage, and try to do the jump Fair to Up B even when it doesn't connect. I'm just tired of the spinning. So much spinning... Make the spinning stop.
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Kirby & Bowser
These two have reasons one may not expect.
I don't know about anyone else, and it might just be my luck; however when I face a Kirby or Bowser on For Glory they absolutely have no idea what they're doing 95% of the time. I'm talking about Kirbys trying to charge his hammer the entire match trying to hit you with it and failing every time, or typical Stone spam. Same with Bowser. Down B for days with a 100% failure rate.
As for the other 5%, they're a blessing to come across. I wish I came across the 5% more than the 95%. The disappointment is real.
Pikachu
I will admit it's very rare for me to find a Pikachu online. When I do find one they're almost ALWAYS good or at the very least make the match last almost about the entire five minutes. He's just so... Small and hard to hit, plus I have zero knowledge on how to deal with him given the fact he's so uncommon to come across. So he gives me an abnormally hard time each and every time.
Ness
I love a good Ness player that doesn't rely on PK Spam every single waking second. Sadly I have better chances at winning the lottery than coming across those types of Ness's. What's been eating at me most of all with Ness specifically lately, is the fact everyone and their dog have been switching to him as a Counter Pick for my Bayonetta. He's almost always guaranteed to come out whenever I play Bayonetta, even when it's clear the person has no idea what they're doing and even did worse using Ness.
I haven't quite studied Bayonettas poor Match Ups yet, but does Ness give her that much of a hard time? Why is everyone suddenly using him as an immediate Counter Pick for her? Aside from that... Ya know.... PK FIRE! PK FIRE! PK FIRE! PK FIRE...!