One idea could be a story where Martha May discovers the Grinch's kind heart long before the events of the original story. Maybe she stumbles upon him secretly helping a lost Who in the forest and realizes there's more to him than his gruff exterior.
A prevalent theme could be the clash of personalities. The Grinch is, by nature, cynical and grouchy, while Martha might be more positive and kind - hearted. Fanfictions could focus on how they deal with these differences, whether they learn to accept each other as they are or if one of them changes to better fit the other. There might also be themes related to the power of love to overcome obstacles, like the Grinch's insecurities or Martha's family and friends not approving of their relationship at first.
Well, another place could be Tumblr. There are often fanfic communities on Tumblr where people share or recommend fanfiction. You might need to use relevant tags like #Grinch #Martha #fanfiction to narrow down your search. Sometimes, the Tumblr search can be a bit tricky, but it's worth a shot.
You can start by having them interact in unexpected ways. For example, the Grinch could accidentally save Martha May from a small accident in the mountains near Whoville. This would create an initial bond of gratitude. Then, gradually build on their conversations, like the Grinch sharing his views on the Whos' noisy celebrations which Martha May initially dismisses but later starts to understand.
Martha Kent is Clark Kent's (Superman's) adoptive mother, known for her love and support. Martha Wayne was Bruce Wayne's (Batman's) mother, tragically killed in an alley, which shaped Bruce's path. Their stories are different but both have significant influence on their sons' lives.
The Grinch is a fictional character. He is a green, furry creature who lives on a mountain above the town of Whoville. He hates Christmas and decides to steal all the Christmas - related things from the Whos in Whoville.
The Grinch is purely fictional. He's become a beloved character in children's literature and media, but he doesn't exist in reality. His antics and personality are all part of the fictional world.
The Grinch is purely fictional. It was made up to bring joy and tell a heartwarming tale during the holiday season. There's no basis in real events or people.