Fanfiction.net is also a possibility. It has been around for a long time and has a wide range of fan-created content. Just use the search function and type in 'Merida x MacGuffin' to see what comes up.
You can try looking on popular fanfiction websites like Archive of Our Own (AO3). It has a large collection of fanfictions from various fandoms, so there's a good chance you'll find some Merida x MacGuffin stories there.
There might be a fanfiction where Merida and MacGuffin team up to save their kingdom from an unknown threat. They could use their individual skills - Merida's archery and MacGuffin's charm - to defeat the enemy. For example, MacGuffin could charm the enemy's spies while Merida takes them out from a distance with her arrows.
You can find them on Archive of Our Own (AO3). It has a large collection of fanfictions, and you can easily search for Merida x Hiccup ones using the search bar.
Another option is to check out Tumblr. There are often fanfiction communities and blogs dedicated to sharing and discussing different fanfictions. You might be able to find some Fem Hiccup x Male Merida fanfictions there, or at least get some leads from the community.
You can try fanfiction websites like Archive of Our Own (AO3). There are often a great number of Hiccup x Merida fanfictions there. Just use the search function and type in 'Hiccup x Merida' to see a list of relevant stories.
One common theme could be adventure. Since both Merida and Macguffin are from a world full of action and challenges, fanfictions might revolve around their joint adventures.
I'm not sure of specific 'brave merida and young macguffin fanfiction' stories off the top of my head. But you can try searching on fanfiction websites like Archive of Our Own. There might be some great works there created by fans who are really into this pairing.
You can start by looking on fanfiction platforms like Archive of Our Own (AO3). It has a large collection of fanfictions across various fandoms. Just type in 'Male Merida x Reader' in the search bar, and you'll get a list of relevant stories. Another option is Fanfiction.net, though the interface and tagging system might be a bit different. You could also try Tumblr, where some users share and recommend their favorite fanfictions.
You can try searching on fanfiction platforms like Archive of Our Own (AO3) or FanFiction.net. Just type in 'Merida and Hiccup pregnant' in the search bar, and it should show relevant fanfictions if there are any.
You can start by looking on popular fanfiction websites like Archive of Our Own. They have a wide range of fanfictions and you can use the search function to specifically look for fergus x merida lemon ones.
Some social media platforms like Tumblr can also be a source. There are often bloggers who are into fanfiction and might post or reblog stories about Merida and Young Macintosh. However, the search on Tumblr can be a bit tricky as it's not as organized as the dedicated fanfiction sites.