Artificial difficulty. "Hmm... this game's too easy... let me just turn the difficulty even higher." And then it just raises the enemy's health and damage but they're still as dumb as a sack of bricks or still have no real ability to fight back against the player's control. It's done nothing but make the game take longer to complete. And usually when I complain about specific games about this, fans usually say something stupid like "Oh just use the first weapon! that makes it even harder!" No, it just makes it take even longer because you're just taking more hits to kill something. It's still stupid and can't fight back.
Memory games. Being forced into an unknown situation where you have to do everything just right or else you lose a fair bit of your health or even die. It seems to give people the false sense of 'difficulty' but really it's just unfair. Typically followed by a gentle tap on the wrist and then you get back to that point knowing what's coming. Yes, I love repeating the same area of a game making another like 20% progress through it each time I die. Because it makes me feel smart with all my hindsight. And then I can just 'go back in time' and do it right. Amazing. I'm good at the hardest of video games. Let me just pat myself on the back from this free gratification. This applies to both those IWTBG wannabes (but not IWTBG itself, as it's more mechanical difficulty. Talking more about the ones where you try and do something, and yet something bad happens out of nowhere with no former information that it would happen.), probably a majority of the 'kaizo' mario mods, as well as Dark Rolls.
Guitar Hero disguised as a fighting game. Fighting games should be about constant pressure and quick reactions in every given moment. Unfortunately, most of them seem to revolve around doing combos. Short technical combos are fine. But "oh stuff I got hit time to go get a drink while he does his 85 hit combo I can't do anything about" isn't very interactive. Sure, it's impressive that the player knows this combo and memorizes how to do it. But is that really a fighting skill? You're beating around a helpless body by essentially playing guitar hero with a controller. This is why I like games like Soul Calibur. There were some old F2P action games that were fun to play too but as the years passed they became overwhelmed with pay 2 win mechanics. Like Rakion and S4 League.
And last but definitely not least.
RNG. Some level of randomness is fine. Damage ranges (like... hey this weapon does 54-73 damage), 50% damage crits. Weapon recoil/spread. Loot tables. World events. Or anything that doesn't directly affect gameplay. As long as you're not paying real money for it. forget lootboxes, gacha, and all that other bullstuff. If you're paying for something you should know what you're getting.
But other randomness is just frustrating. Powerful crits can ultimately destroy someone's strategy. "Ah, he's going to do this and then I can just do this... Nope. Got a crit, I'm just loving dead." All due to a computer pulling up a number based on arbitrary stuff it pulls from things not even related to the game itself. "Oh sweet, I can just hit this... nope... 93% chance to hit and it completely missed." You've done everything right, potentially even capitalizing on an enemy's mistakes, only to get punished for it in the end. Which is a really, really, really bad design flaw. You're supposed to punish people for doing things wrong, so that they learn from their mistakes. Punishing someone for doing something right could make them perform worse later. Subconsciously they could feel like that they need to do it differently next time, despite it being a good play. And crucial game objectives too. "Gee, I have no idea where this next objective is going to be, I sure hope I'm in the right place." And it's on the other side of the map. I can't remember any examples of this, but there are some.
