One great Leviathan - themed 'Supernatural' fanfiction is 'The Leviathan Chronicles' on FanFiction.net. It delves deep into the nature of the Leviathans and their interactions with the Winchester brothers in a very engaging way.
A really creative plot is in a fanfic where the Leviathans can possess animals as well as humans. It makes for some really strange and unexpected encounters for Sam and Dean.
Characterization is key. Since Leviathans are complex creatures in the Supernatural world, a good fanfiction will develop their characters well. For example, showing their intelligence and cunning. Another element is plot. It should be engaging and perhaps explore new aspects of the Leviathan lore that the show might not have fully covered.
One popular Leviathan Supernatural fanfiction is 'Leviathan Rising'. It delves into the origin and unique powers of the Leviathans in a really engaging way. The author does a great job of creating a tense and thrilling atmosphere throughout the story.
The 'Underworld' novels are great too. They are set in a world where vampires and werewolves are in an eternal war. The stories explore the complex politics within each group, as well as the history of their feud. It has a lot of action and interesting characters on both sides.
Well, in 'Twilight', the vampire lore is centered around their super strength, speed, and the fact that they sparkle in the sun. It's a unique take. However, 'The Vampire Diaries' novels have a more complex vampire society with different vampire clans, and their powers are more diverse. So, I'd say 'The Vampire Diaries' has a more interesting vampire lore.
One great vampire supernatural fanfiction is 'The Vampire Diaries' fanfics. There are numerous stories that expand on the show's universe, exploring different relationships and plot twists. For example, some focus on alternate endings for the main characters' love stories.
One classic is 'Dracula'. It's about a man, Van Helsing, and others facing the powerful vampire Dracula. Another is 'The Strange Case of Dr. Jekyll and Mr. Hyde', where Dr. Jekyll battles his own dark, supernatural alter - ego.