When it comes to legendary resistance, I just roll the dice and say the target made their save, at least most of the time. Other times I like to flavor it with the head goblin grabbing a minion and interposing the minion at the last moment or similar which makes it more interesting as minions scramble away.
Definitely PCs being knocked out of the fight can be not fun. If it's guaranteed to be for the entire combat you can hand them a monster and let them kill their fellow PCs. But if it's just bad luck that they keep failing a save? That's rough. On the other hand, I don't want to totally avoid those options either. I do tend to switch up spells, even if I change that spell/ability that will have the PC sitting on the sidelines be dominated. Killing fellow PCs is more fun than twiddling your thumbs.
Other things that are not fun? Arguments at the table. I just shut it down when I'm DM. I'll listen, but then make a ruling to keep the game going. We can chat after the game unless of course it will make a dramatic difference in the moment.
But I also think always saying yes or always succeeding is not fun, at least not for me. Sometimes I want to be told I can't do what I was thinking, it forces me to think outside the box and come up with alternatives. I had a high level rogue with reliable talent, it was kind of boring when I knew I couldn't fail certain tests. Being frustrated now and then makes it more special when something else does work.
Anyway those are the things off the top of my head.
Definitely PCs being knocked out of the fight can be not fun. If it's guaranteed to be for the entire combat you can hand them a monster and let them kill their fellow PCs. But if it's just bad luck that they keep failing a save? That's rough. On the other hand, I don't want to totally avoid those options either. I do tend to switch up spells, even if I change that spell/ability that will have the PC sitting on the sidelines be dominated. Killing fellow PCs is more fun than twiddling your thumbs.
Other things that are not fun? Arguments at the table. I just shut it down when I'm DM. I'll listen, but then make a ruling to keep the game going. We can chat after the game unless of course it will make a dramatic difference in the moment.
But I also think always saying yes or always succeeding is not fun, at least not for me. Sometimes I want to be told I can't do what I was thinking, it forces me to think outside the box and come up with alternatives. I had a high level rogue with reliable talent, it was kind of boring when I knew I couldn't fail certain tests. Being frustrated now and then makes it more special when something else does work.
Anyway those are the things off the top of my head.