Writing an 'mtg lemon fanfic' is no easy feat. Firstly, immerse yourself in the Magic: The Gathering world. Read the official materials, play the game if possible, and interact with the fan community to get a feel for the essence of the franchise. For the 'lemon' part, it's about adding a layer of romantic or more intimate relationships to the story. But this has to be done tastefully. You can't just throw in adult - themed content without any context or purpose. Develop your characters well, give them motives and backstories that justify their actions in the story. Also, when it comes to the more adult - like content, make sure it adheres to any rules or guidelines of the platform where you plan to share your fanfic, if at all.
If you want to write an 'mtg lemon fanfic', start with the basics. Familiarize yourself with the rules, creatures, and spells in Magic: The Gathering. Then, for the 'lemon' aspect, you need to be able to write about relationships and emotions in a more sensual or romantic way. However, this is a tricky area as it can easily cross into inappropriate territory. You should also study some good examples of fanfics in general to get an idea of pacing, character development, and how to build tension in your story. And always remember to respect the source material and the community's standards.