Concept: The body of one magician is in fact connected permanently to the deck that he uses for performing.
Sketch
Mark and Loki live together. They are both magicians. Loki is in the shower. Mark is hurrying to his first magic performance in years. In a rush, he by accident takes Loki's deck instead of his.
When Loki gets out of the shower and starts dressing, Mark is seen to arrive at the show, but in his pocket the deck goes through many changes as Loki puts on different clothes.
Mark arrives where he is expected to perform. At this stage it has been established that the Loki and his deck of cards are connected. What Loki does has a direct effect on how the deck behaves.
While Mark starts performing with the deck, quite supernatural things start happening without his seeming control of them. To the audience, it all appears like a planned and quite astonishing show!
Ideas
When Loki stretches his body, the deck bends inwards and outwards.
When he spits the toothpaste into the sink, a card comes out of the deck.
When he takes things out of his pockets, the deck starts producing objects.
When he sneezes, the deck springs from one place to another.
It depends on how realistic you want to keep it, or how crazy you want to make it look. If you're going for a Key and Peele type of short, you can go as far as Loki being an actual magician/god, and transforming in different animals, levitating objects, meanwhile all of this influencing Mark's performance.