While walking back from the last door to the house they had just knocked on as trick or treaters, Merlin and Arthur were making their way home in their Halloween costumes. Arthur had gone dressed as Frankenstein while Merlin had to make do with a smurf costume, which he wasn't too pleased about.
"I can't believe I am actually walking through the neighborhood in a smurf costume" Merlin moaned as he poked the costume in the center of his chest.
"Shut up Merlin" Arthur began before adding; "Besides blue suits you "along with a small smile.
"Ha- ha "Merlin replied sarcastically.
At that moment Merlin decided to turn the tables on Arthur.
"I must say that mask makes a massive improvement on how you usually look" Merlin commented while one of his huge grins spread across his face, almost instantly irritating Arthur.
But to Merlin's dismay his irritation didn't last long as he was laughing loudly soon afterwards and making a pathetic attempt to cover up his laughter.
"Sorry Merlin but I can't take comments like that seriously from a smurf" Arthur chuckled before once again exploding into laughter.
"Prat "Merlin whispered under his breath before finishing off with "just you wait till next Halloween".
The same time on the following year, Merlin had bought his and Arthur Halloween costumes but he hadn't let Arthur see his until that very afternoon on the day of Halloween.
Merlin had rushed out of his room first in his superman costume just to see Arthur's reaction to his costume. Merlin was leaning against the wall in a huge laughing fit when he saw Arthur come out of his room, folding his arms at Merlin's reaction.
"It's not funny Merlin"! Arthur bellowed as he jabbed at his costume with force.
In between taking large breathes from his laughter Merlin responded with, "Sorry I can't take comments like that seriously from a Genie"! Merlin was then staggering over to the front door, still laughing at Arthur and his hilarious costume.
Arthur glared at Merlin with pure anger before taking a deep breath and getting the evening over and done with.
As they both walked out of the house, Merlin thought to himself; last year I may have been the trick but this year I will definitely be getting the treat.
(Just to note there is an image of the Genie costume that Arthur wears but you will be able to access it on Archive of our own in the Merlin part of the fandom with the same name as the title shown on this fiction.)