What do you think is the most annoying boss fight in any game you have made. I'd say all iterations of Kushala Daora from Monster Hunter. It basically abuses the wind pressure mechanics, where if you get slapped by wind from a monster (such as when it flaps its wings), it knocks you back a bit. Kushala Daora takes that one step further and has an aura of wind surrounding it, which covers pretty much all of it except for the tip of its tail, some of its wings, and its head. Basically covers 95% of the monster's body. It makes it so that melee weapons can't hit it effectively without being blasted back, and bow arrows and bowgun shots cannot even hit that area because it basically deflects them. Also, the freaking tornadoes are goshdarn annoying, and sometimes they torture my Xbox One (I have the normal Xbox One). In most MH games, a poison weapon is required to fight it, because poisoning the monster also makes the wind aura go away.
An image of Kushala Daora:
I honestly like the idea of a dragon capable of controlling wind, but Kushala Daora is exactly the wrong way to implement it into mechanics. It's fight is annoying, and in World, poison weapons no longer stop the wind aura, a weapon mechanic known as elderseal does, which I think that is kinda dumb, or could be used at the same time as elderseal. Elderseal basically lets you cancel out certain abilities of monsters of the Elder Dragon classification in Monster Hunter World and Monster Hunter World: Iceborne.
An image of Kushala Daora:

I honestly like the idea of a dragon capable of controlling wind, but Kushala Daora is exactly the wrong way to implement it into mechanics. It's fight is annoying, and in World, poison weapons no longer stop the wind aura, a weapon mechanic known as elderseal does, which I think that is kinda dumb, or could be used at the same time as elderseal. Elderseal basically lets you cancel out certain abilities of monsters of the Elder Dragon classification in Monster Hunter World and Monster Hunter World: Iceborne.