Perhaps a plot where Rose gets to travel with all the Doctors at once. They could be facing a powerful enemy that only their combined skills and knowledge can defeat. This would lead to some hilarious and also very tense moments as they all try to work together while also dealing with their own egos and different ways of doing things.
One interesting plot could be Rose's unique reactions to each Doctor's distinct personality. For example, with the Ninth Doctor, she might be more in awe of his newness to her world. With the Tenth Doctor, their deep emotional connection could lead to adventures filled with heart - wrenching decisions. And with the Eleventh Doctor, her experiences could be more whimsical and full of unexpected twists.
The main character is Rose. She is the one around whom the whole 'meets all the doctors' concept revolves. As for the Doctors, they are the key characters too. They have different personalities and backstories. The Ninth Doctor, who is still dealing with the aftermath of the Time War. The Tenth Doctor, with his complex relationship with Rose, and the Eleventh Doctor, with his unique style of adventuring. Their interactions with Rose are what drive the story forward in this fanfiction.
One interesting plot could be Rose and the 11th Doctor getting into a time - related mystery. Maybe they end up in a time loop and have to figure out how to break it together. Another could be them encountering a new alien species that challenges their understanding of the universe.
One interesting plot could be the rose character having to prove its uniqueness and value among the thorns. Maybe it has special powers that the thorns don't understand and it has to use those powers to protect the group of thorns from an outside threat.
One interesting plot could be Ruby and Oscar having a training session in a secret garden within the Rose Garden. They could be working on new combat techniques and sharing their insecurities about their roles in the fight against Salem. Another plot might involve them finding a rare Grimm - like creature that is actually a guardian of the Rose Garden and has to be befriended rather than fought.
Another interesting plot could be Rose's discovery of Draco's past and how she helps him come to terms with it. She might find out about his family's dark history during the wizarding wars and be a source of light and forgiveness for him.
A really cool plot could be that Gohan and Naruto get transported to an alternate dimension where they have to find a way back home. Along the way, they meet different versions of their friends and foes, and they have to work together to overcome the challenges of this strange new world. They might also discover some secrets about their own powers and the nature of their universes in the process.
One interesting plot could be Rocket and the raccoon going on an intergalactic adventure together, facing strange alien creatures and solving mysteries along the way.
There could also be a plot where Magnus and Max are from different dimensions or time periods and accidentally meet. At first, they don't understand each other because of the differences in their worlds. But as they start to communicate and learn about each other's cultures and powers, they find common ground. They might have to work together to find a way to get Max back to his own time or dimension, and in the process, they create memories and a relationship that changes both of them for the better.
One possible plot could be Thea and Barry teaming up to solve a mystery in both their cities. Maybe there's a meta - human causing trouble in Star City and also has some connection to Central City's problems.
One interesting plot could be Sonic and Maria teaming up to save a parallel universe. They use Sonic's speed and Maria's intelligence to overcome various obstacles.