I've discovered something relatively new I hate, mostly because of encountering it in one game where it is implemented in the worst possible way. Enemies that can apply status effects by simply being in proximity to them without needing to first hit with an attack. There's a few games I can think of that do this but I've only encountered one recently where it turns the game into hot garbage.
Sekiro has bosses where your movement is slowed down, preventing you from running and forcing you to get used to the slower movement and sword swing speed. They're undead and spooky, so it's a feature of the arena more than anything. An annoying gimmick perhaps to learn to deal with, but not bad design.
Tales of Destiny 2 has a boss that activates a poison aura when his HP drops low enough, and where HP drains when in proximity. This (and other fights) can be managed by having a dedicated healer in the back, and the fight's conveniently setup so your team naturally has this. The HP drain is also manageable with items, or you can just be awesome and
beat him without taking damage by never letting him get into range.
Both of these are good ways of implementing this as boss-specific gimmicks.
What's
not good, as in outright annoying, is what a fan-made expansion pack for Risk of Rain I've tried recently does, called Starstorm. It introduces several new elite type enemies (where normal enemies are buffed with an attack element that gives them special properties). Originally, you had flaming and shocking enemies that could damage you by being close, as in right next to your character. Their damage was manageable and you could dodge them easily enough. The expansion adds new elite types, three of which have undodgeable auras (no attack animation to escape from) which immediately hit you if you happen to wander close to one.
The first are black enemies that inflict a weakness aura simply by being close to them. It seems to reduce your damage output slightly, but not enough to be a major threat. Fine, I guess.
The second are enemies with glowing orbs above them that can fire instant hit laser beams. They hit you if you aren't moving to evade the beam, and considering most of the cast has to stop to attack, they can be rather dangerous if you accidentally stop moving when in range.
The third type with an unavoidable aura is
literally the worst designed enemy in any platformer I've played ever. Not exaggerating, they're extremely off-putting and using the unlockable tweak options to disable the new elite types just to turn them off is probably the best way to enjoy the fanmade expansion pack. They inflict a "void" debuff. This
utterly cripples your movement speed and jump height to the point of being negligible. It looks like if you have a ton of horizontal movement boosting items, you can overcome some of the speed reduction and escape, but even with multiple jump boosting items your jump will be unable to escape the short 1-tile high ledges everywhere. If you accidentally run into a void enemy over a small pit, you will literally be unable to escape and will get almost immediately swarmed unless you can kill the void enemy. It gets even better though; their aura is hilariously massive. If you try to attack them from above or jump above them, their aura is large enough that they can lock you down in the air, causing you to float very slowly and be a massive target.
Risk of Rain is a 2D game where the level design often forces you to double-back through enemy crowds, trying to mitigate damage and not get caught as you rush through them via tight hallways. The void elemental enemies that can randomly spawn are horrible and go against the spirit of the game, which originally only had two attacks that could slow you down: a short ranged spit attack from an enemy that made you a bit slower if it hit, and a shockwave attack from the final boss that stuns you if it hits (which can be jumped over). They are quite literally the most dangerous enemies in the game, and by a significant margin. And, they appear at random, and can be difficult to see if the enemy that gets the void element is small and in a crowd of like 30 enemies or so since the aura isn't big and glaringly obvious.
Void elemental enemies feel built to be dealt with a massive quantity of mobility items and drones, the sort of thing you'd normally have at the point where you're mostly unstoppable. Even then they're still annoying since you're running around and suddenly having your movement crippled by something you can barely see. But, due to the random nature of the item drops, if you encounter one early on or during a run where you're just headed to the final boss without looping and haven't found any mobility items, they can be fatal to a run as has happened to me multiple times. And not getting mobility items is more likely to happen in Starstorm due in part to the expanded item pool that includes a lot of questionably useful items. The Command artifact where you can pick what you get seems to be a lot more useful in Starstorm.
Proximity based movement debuffs that immediately cripple your movement speed and make you essentially unable to jump suck, especially when given out to randomly appearing enemies in a game where it can be hard to quickly spot individual threats in a large crowd. That's just bad design, and hard in the worst, most unsatisfying way possible. Even if the enemy had to hit you to inflict it it'd still be nasty, but nowhere near as bullshit as it is that an enemy can essentially kill you by wandering near you.
The game balance in Starstorm, especially the new Typhoon difficulty, is basically a mess. The difficulty largely from the danger of getting screwed over by sheer RNG rather than your own ability to dodge attacks, and the hard stuff is hard in largely uninteresting ways. The void portals you can enter have nothing but void enemies, forcing you to use the ropes to cheese the enemies slowly but safely since fighting them on the ground reduces you to near immobility. It may be intended that you avoid void portals until you've looped multiple times and have items stockpiled though, because entering a void portal can trigger nemesis enemies who basically come with a ton of random items and use them againdt you, rushing in and being near unavoidably once in their aggression range. It's like they're designed to be the only thing capable of threatening a player stockpiled with tons of items, but can be encountered long before that point for some reason, and it's more like an RPG where whether you win or lose is down to if you happen to be strong enough before meeting them. Gah.
These sort of game balance issues that feel like they thoughtlessly throw new content at a game with little regard for the original game's design choices are why I generally avoid fan made expansion patches...