Decided to try arcade mode on "Ridiculous" difficulty, one step up from hard, which I could usually clear with my team of Filia and Squigly. First match on Ridiculous, the game pits me against Double. A single Double. 2v1.
I HATE fighting Double. I hate everything about Double. I hate her design, I hate her moves, I hate her AI, everything. You know why? Because it constantly WRECKS MY SHIT YOU STUPID CHEATING AI BASTARD WITH YOUR GUN AND YOUR HIT CONFIRMS AND YOUR COMBOS AND SUPERS AND JUMPING AND AAAAAUGH INFURIATING.
Lost the match with Double still at half health, retried, beat her with literally a pixel of health left on Filia after Squigly got ko'd. On to the next match, guess what, ANOTHER ROUND OF ANOTHER DOUBLE. And Eliza. And Beowulf. The three AIs I have the hardest time against. BUT ESPECIALLY DOUBLE.
I forfeited the game. Screw you too, rng. The arcade run probably was Double all the way down.
Double at any difficulty loves to hit confirm her Luger Replica into Bandwagon Rushdown, because it's so absurdly damaging, especially as a solo character. It also has invincibility frames during the entire time Double is summoning and using the Bandwagon. If you reckon you're gonna have a tough time, abuse assists with super armor (eg. Robo Fortune s. HP, Collimating Saw, or Cerebella's QCF+MP, Lock and Load, Eliza's crouching HK which I can't remember the name or Big Band's Brass Knuckles HP or MP).
Double has a lot of unique properties that make her one of the most infuriating opponents to fight - her small airsize making her able to drop out of air combos, hurting Filia and Fukua's game against her, the ability to shut down projectile spammers/zoners like Fukua, Peacock and Robo-Fortune with Flesh Step (a command dash that has a few invulnerability frames, so well timed a Double player can Flesh Step through smaller projectiles though not through larger or multi-hit ones that stay active a long time.) Also, Luger Replica is very fast travelling and can punish the slower characters like Cerebella or Big Band, though Cerebella can reflect the shot, she needs very good timing, and the CPU Double almost always goes for a Bandwagon Rushdown after Luger Replica.
To date, playing on any difficulty, up to and including Nightmare, I've never seen CPU Double rely on ANY supers besides Bandwagon Rushdown, because it's just so good. (high level double players forced to use her as a point character will prefer Catellite Lives as it makes every single attack Double has become safe on block, and the hits from the catheads don't add to IPS.) Same with CPU Cerebellas, where a solo Cerebella against a trio can deal ~50% hp with a basic hit confirm into Ultimate Showstopper (although it leaves a significant, almost all the health dealt recoverable as red damage.)
Tl;dr, certain CPUs are horrific to fight on high difficulties, solo Double, solo Cerebella, duo or trio Peacock.