Dr. Eggman might also be a part of the story. He's the main antagonist in the Sonic series. His evil plans could be the catalyst for Sonic and Shadow's encounter. Whether it's stealing chaos emeralds or creating some new doomsday device, Eggman's actions could force Sonic and Shadow to interact and either fight against or alongside each other.
In such a fanfiction, they might start as rivals. Sonic, with his speed and carefree attitude, could initially clash with Shadow's more brooding and serious nature. For example, they could compete in a race across a fantastical landscape filled with loops and obstacles. Sonic would be in it for the thrill, while Shadow might see it as a test of his own abilities.
You can try fanfiction websites like Archive of Our Own (AO3) or FanFiction.net. They have a wide variety of fanfictions, including those about Sonic meeting Shadow.
Dr. Eggman could be a great main villain. He might have a new plan that involves both the power of Sonic Underground's music and the Chaos Emeralds that Shadow guards. He could try to create a device that amplifies negative emotions through music and uses the Chaos Emeralds' power to spread chaos everywhere.
One idea could be that Sonic Underground's siblings get separated in a new zone and Shadow accidentally stumbles upon them. He initially thinks they are enemies but then realizes they are on the same side against a common foe. Another could be that Shadow is on a mission related to the Chaos Emeralds and crosses paths with Sonic Underground. They end up having to team up to stop a new villain who wants to use the power of music and the Chaos Emeralds for evil.
Another reason is the creativity of the plots. Since it's fan - made, there are no real boundaries. A story could combine elements from different Sonic games or even introduce entirely new concepts. For example, a fanfic could have Shadow and Silver discover a new form of Chaos energy that changes the power balance in their world.
Tails is a very popular character to include. He is Sonic's best friend and his technical skills can add a lot to the story. For example, he could help Sonic and Shadow figure out some complex machinery or technology that is part of the plot.
Yes, there are quite a few out there. Some can be found on popular fanfiction websites. You might need to search through the Sonic the Hedgehog fanfiction section specifically. However, the quality can vary greatly.
One great aspect of Sonic Shadow and Silver fanfiction is the exploration of different character dynamics. Writers often create unique relationships between these characters that we might not see in the official games. For example, they could show Shadow and Silver teaming up in a new adventure, facing challenges that test their skills and friendship. Fanfiction also allows for the expansion of their backstories. Maybe Silver's time - traveling abilities are explored in more depth, or Shadow's past traumas are delved into in a way that gives a new perspective on his character.
In the world of 'Shadow and Sonic Fanfiction', 'The Lost Memories' is a must - read. It's about Sonic losing his memories and Shadow having to help him. The story does an amazing job of exploring their relationship in this difficult situation. 'Sonic's Darkest Hour' is another one where Shadow comes to Sonic's rescue in a really unexpected way. Also, 'Shadow and Sonic: The Race for Power' is engaging as it pits them against each other in a new kind of power struggle.