Not necessarily. There are many fictional characters with incredibly powerful abilities and it's hard to say for sure if Doom Slayer is the absolute strongest.
Well, 'Doom Slayer: Redemption' is a great fanfic. It shows the Slayer's struggle with his own inner demons while still fighting the literal demons. Then there's 'The Doom Slayer's Allies'. This fanfic explores the relationships the Slayer could have with other characters, whether they be human survivors or other powerful entities. And don't forget about 'Doom Slayer: In the Wasteland'. It's set in a post - apocalyptic world where the Slayer has to face not only demons but also the harsh environment.
There are definitely some 'Goblin Slayer x Doom' fanfics. One interesting aspect that some of these fanfics explore is the different combat styles of the two main characters. The Goblin Slayer is more methodical in his approach to dealing with goblins, while the Doomguy is all about brute force against demons. In a crossover fanfic, seeing how they would either learn from each other or clash because of their different styles can be really engaging. Also, the settings of the two can be blended in unique ways, like the dark and gritty world of 'Doom' with the medieval - ish setting of 'Goblin Slayer'.
Well, the plot could involve a rift opening between the two worlds. Goblins start pouring into the Doom world and the Doomguy has to deal with them. Meanwhile, the Goblin Slayer follows the goblins through the rift and they end up working together to close the rift and stop the chaos. They might exchange combat techniques and learn from each other's experiences along the way.
First, know the lore of Doom well. Understand the Doom Slayer's character, his abilities, and his purpose. Then, come up with an interesting plot. It could be something like the Slayer facing a new type of demon or exploring a new dimension. Next, create some engaging characters to interact with the Slayer. They could be allies or foes. And don't forget to write in a way that captures the action - packed and dark atmosphere of the Doom universe.
It's fictional. The story was crafted by the writer to entertain and engage readers rather than being based on real events. Many elements in it are imaginative and not drawn from actual happenings.