I want to give this a try. Let's workshop a snippet:
“Wait, you’re magic?” said Arthur, staring at Merlin. He flinched, and dropped the goblet of wine he was holding. Merlin looked fearfully back at Arthur. Then Merlin looked annoyed.
“Yes,” said Merlin.
“Why did you say it like that? And are you going to clean up that wine?” said Arthur.
“So all those near-death experiences that you magically got out of…” said Merlin, in disbelief.
“I’m lucky!” said Arthur.
“No one’s that lucky,” said Merlin.
“So… it was you, doing all of that? Even though it put you in danger?” said Arthur. Then Arthur took a step closer to Merlin. He was soaked, and Arthur saw him shiver.
So... this feels little repetitive, and it's not always clear who "he" is referring to. This is a classic example of the type of things people 'fix' with antonomasia and epithets:
“Wait, you’re magic?” said the prince, staring at his manservant. The brunette flinched, and dropped the goblet of wine he was holding. Merlin looked fearfully back at Arthur. Then the smaller man looked annoyed.
But there are other (better) ways to do this, and I really like @arkadijxpancakes list, so I'm going to see if I can use all of them.
1. Switch up sentence structure.
All of these sentences have a character as the subject, and so the first word of every sentence is 'Name' or 'He.' Consider mixing it up:
Staring across the throne room, Arthur said - “Wait, you’re magic?" A clatter, as the goblet Merlin was holding fell to the ground. Fearfully, he looked up at Arthur. Then his expression changed into one of annoyance.
Can be a fix for repetition, but can also help with tone.
“Wait, you’re magic?” said Arthur. Merlin's face went white. His hands shook, and the goblet he was holding went clattering to the ground. He looked fearfully back at the throne. There was silence in the massive room. Then Merlin's expression slowly changed into one of annoyance.
In this case, bringing up the throne and and size of the room communicate that Arthur has the power in this situation.
You can also essentially use actions as dialog tags.
“Wait, you’re magic?” Arthur twisted himself around in the throne to see Merlin better. Merlin was frozen. The goblet in his hands looked like it was about to fall from his limp fingers.
"Yes..." Then the cup did clatter to the ground. "Yes," Merlin said again, only now he sounded annoyed.
4. Dialog tags don't have to go at the end, and they don't have to go on every piece of dialog.
I like to use dialog tags almost as commas or periods, to communicate a pause or a change in subject.
“Yes,” said Merlin.
“Why did you say it like that?" said Arthur. "And are you going to clean up that wine?”
Merlin looked at him in disbelief. “So all those near-death experiences that you magically got out of…”
“I’m lucky!”
“No one’s that lucky."
“So… " Arthur said. "It was you, doing all of that? Even though it put you in danger?”
5. Stick with one POV character at a time.
One of the things that is making my original example a little confusing is it's not super clear who my point of view character is. But, let's just say - it's Arthur, we're going to be looking through Arthur and only Arthur's eyes this scene. That does a lot of my work for me:
“Wait, you’re magic?”
Merlin flinched at his voice, something he hadn't done in years. The goblet he was holding fell to the ground, and for a second he looked terrified. Arthur hated it. Then Merlin's expression went back to his much more normal annoyed, and Arthur relaxed.
6. Use action to identify character
“Yes,” said Merlin.
“Why did you say it like that? And are you going to clean that up?” Arthur pulled his feet up onto the throne so as not to stain his shoes.
“So all those near-death experiences that you magically got out of…” Merlin had produced a cloth from nowhere, and was now down on his knees, mopping up wine.
“I’m lucky!” Arthur drew back from the sheer intensity of Merlin's cleaning.
“No one’s that lucky." More angry scrubbing.
7. Structing actions around character.
“Wait, you’re magic?” said Arthur.
Merlin flinched, dropped the goblet he was holding, and looked fearfully back at Arthur. Then started to look annoyed.