A really creative plot in 'Straw Hats Time Travel Fanfiction' is when they time travel and become part of the ancient prophecies. So, they are seen as the heroes or villains depending on how the locals of that time period interpret them. They have to either fulfill or change the prophecies while also dealing with the time - travel paradoxes. Also, there are fics where the Straw Hats time travel to a world where the Devil Fruits don't exist. They have to rely on their pure physical and mental skills to survive, which is a big change from their normal adventures.
Well, some of the most creative plots involve the Straw Hats time traveling to different dimensions during their time travels. In these dimensions, the rules of the One Piece world are completely different. For instance, in one dimension, the sea is made of sand and they have to find a way to sail on it. Another creative plot is when they time travel to a time where the Straw Hats were never formed. They then have to find a way to bring the crew together again, but with the added challenge of the different time period's circumstances.
One creative plot is when the Straw Hats time travel and end up changing the entire One Piece world's history. For example, they might accidentally prevent a key event from happening, which then creates a completely different future. Another is when they time travel into the dreams of their crewmates. In the dream world, they have to deal with manifestations of their friends' fears and desires while also trying to find a way back to reality. It's a really trippy and interesting concept.