Most hated enemies in games.

The one that routinely frustrates me is the self-destruct kind of enemy that chases you down in a kamikaze fashion and blows up in your proximity, usually erasing you in that one instance. One little slip-up and you can replay whole sections.
Now if their arrival is properly telegraphed, like in Serious Sam ("aaaaaaaaAAAAAAAAAAA!"), I can live with them and they could work very well. But when there is little to no telegraphing of their arrival it gets old really fast.

Stunlocking enemies are the worst: If I die to an enemy that was designed to be either fair or extremely punishing but also counterable then fine, I say that was my fault.

But when the enemy straight up stunlocks you (especially when it happens without any indication) without any chance of retaliation then I really, really dislike that: Bonewheels from the original Dark Souls are the perfect example: not only they stunlock and drain your stamina until you die, they are also extremely fast, there is like 6 of them rolling around anywhere at any given moment, their hitboxes are questionable and the area is extremely dark which makes navigating tedious.

Marlboro from Final Fantasy games and specially from FF 10 !

Any better player than me in multiplayer

I'm not good in fighting games, so pratically any of the bosses in KOF, like Rugal Bernstein in 98.

View attached image.

Not really enemies per se, but still one of my most hated video game opponents. Elder Scrolls 3 Morrowind, cliff racers. No matter how many sound enhancing mods I installed, 95% of the time I couldn't hear them untill the bastards were pecking me and flapping their @#$@# wings at me, screeching and all. I was relieved when Bloodmoon came out because I could go to Solstheim where there weren't any fricken cliff racers.
One positive though, all but one of the characters I've ever done playthroughs with have had fantastic marksman skills 😀

I hate immortal enemies like Nemesis in RE3 or couple of creatures in Evil within.

Marauders from Doom Eternal, hands down the most annoying enemy I've faced in a game.
He is constantly immune to damage, has a long-range and close-range attack which you can't hit him through, and a medium-range attack that has a slight opening where you can hit and stun him. He is a massive pain to fight against in general, but a LOT LOT worse when you are fighting multiple enemies and one or even two of them appear.

My second comment here but I remembered about enemies (mostly "bosses") that you are supposed to lose to. It's fine when the game makes it obvious, like in God of War 2, when Kratos gets beat up really bad and goes to fight Zeus for the first time, and when you take control, Kratos barely responds to your inputs. But I've seen more and more games doing this without any sort of telegraph, and you end up just wasting your time and resources (like items) in an impossible battle. It's gotten bad to a point where if there's a really tough boss fight right at the beginning of a game, sometimes I'm not sure if I'm supposed to beat it or not (I've purposefully let myself die a few times in bosses I was supposed to win against). Like, my dev dudes, why not just make the main character lose in a cutscene or something. Cut the crap, guys. Jeez.