For Doflamingo, you can focus on his flamboyant and unpredictable nature. Show his sadistic side in how he deals with enemies, but also explore his more vulnerable moments, like when his plans are thwarted. For Crocodile, emphasize his cool and calculating demeanor. Let his past failures fuel his actions in the fanfiction, like his determination to regain his lost status. Maybe show how Doflamingo's chaos sometimes clashes with Crocodile's order.
Luffy's victory over Doflamingo in the manga was a combination of factors. His growth in strength, his unwavering will, and his ability to adapt to Doflamingo's tactics all played a role. Additionally, the support of his friends was crucial in tipping the scales in his favor.
First, consider their backstory. For example, if your OC grew up in a small island that was once under Doflamingo's control but managed to escape, it would shape their personality. They might be cautious, distrustful of authority, and have a strong will to protect others from a similar fate. Their skills could be related to survival, like being an excellent hunter or fisherman, which they learned during their escape.
I really like 'Doflamingo's Unseen Side'. It presents a different perspective on Doflamingo. It has a lot of action scenes and also explores his relationships with other characters in the One Piece universe in a unique way.
One character that would make for an interesting pairing with Doflamingo in a crossover fanfiction is Zoro. Zoro's strong sense of justice and his skills as a swordsman would clash with Doflamingo's devious ways. They could have epic sword battles, and Zoro might be the one to cut through Doflamingo's strings, both literally and metaphorically. Also, Nami could be paired with Doflamingo. Nami's intelligence and ability to manipulate situations for her own gain, although in a more positive way compared to Doflamingo, could lead to some really interesting interactions. She could try to outwit him in a game of wits.
Well, at first it would probably be full of mistrust. Nami knows Doflamingo's reputation as a cruel and power - hungry man. But as the story progresses, if Doflamingo shows a different side of himself, like protecting Nami from a greater enemy, Nami might start to soften towards him.
To write a good Doflamingo OC fanfic, first, you need to have a solid understanding of the Doflamingo character and the world he exists in. Then, create an interesting OC with a distinct personality, backstory, and goals. Make sure the OC's actions and decisions are believable within the context of the One Piece universe. Also, have a clear plot that involves the OC and Doflamingo in an engaging way.
Finally, use vivid descriptions and good dialogue. Describe their appearances, the settings they are in, and their emotions. Good dialogue can bring the characters to life and show their relationship development. For example, Viola might say something like 'I know you have done bad things, but I see a glimmer of good in you' to Doflamingo, which can start a whole new dynamic between them.
Once Luffy is kidnapped, Doflamingo might try to break Luffy's spirit. But Luffy being Luffy, he would resist. Meanwhile, the crew's journey to rescue him could be filled with many obstacles. They might encounter other pirates or marines who are either allies or enemies of Doflamingo. The crew would have to fight their way through and use their combined skills to reach Luffy. For example, Brook could use his soul powers to pass through walls and scout ahead.