Well, in batman vs justice league fanfiction, characters like Nightwing and Oracle are prime candidates to side with Batman. Nightwing was Batman's first Robin and has a loyalty to him. Oracle, with her intelligence and access to information, would back Batman if she believed his cause was just. Additionally, characters like Batgirl could also side with Batman, especially if she thought the Justice League was overstepping its bounds.
Batman is obviously one of the most popular. He's a complex character with a lot of depth, and in a 'vs' scenario with the Justice League, his skills and intellect are put to the extreme test. Superman is also popular. His god - like powers in contrast to Batman's more human abilities create a great dynamic. Wonder Woman is another favorite. Her strong moral code and combat skills add an interesting element to the story when she's involved in the conflict between Batman and the League.
One possible storyline could be that Batman discovers a conspiracy within the Justice League that endangers Gotham. So he and Robin decide to take on the League to stop it. Another could be that the Justice League is being mind - controlled, and Batman and Robin are the only ones who realize it and try to free their friends by fighting them. Or perhaps there's a misunderstanding where the Justice League believes Batman and Robin have turned bad, and they have to fight to prove their innocence.
Well, in a battle between Batman and Robin vs the Justice League, it's really tough to say. Batman is known for his incredible strategic mind and vast array of gadgets. Robin, depending on which one, also has some skills. But the Justice League has some of the most powerful beings in the DC universe like Superman with his super strength, speed and heat vision, Wonder Woman with her combat skills and Amazonian powers. However, Batman has been known to take on foes much more powerful than him with his wits. So it could be a very close fight if Batman and Robin could use the right tactics.
A possible plot idea is that Batman discovers a dark secret within the Justice League that they are unaware of. This secret could be something that could potentially destroy the League or change their moral compass. Batman then has to decide whether to confront the League directly or try to fix the problem on his own, which causes the 'vs' situation as the League may see his actions as a threat.
It depends on the context. If it's a straight - up fight, the Justice League has superpowers that would seem to give them an edge. But Batman is known for his strategic mind. If he had time to prepare, he could potentially take down members one by one using their weaknesses. For example, using kryptonite against Superman.
One idea could be that Batman discovers a hidden agenda within the Justice League that he believes endangers the world, so he decides to oppose them. For example, he might find out that a new technology the League is using has unforeseen and dangerous side effects.
One interesting plot could be Batman's distrust of the Justice League's unrestrained power leading to a full - on confrontation. He might secretly plan to take down each member one by one, using his intellect and prep time. Another could be the Justice League being mind - controlled and Batman having to fight them to break the control.
Batman's sacrifice would likely have a huge impact on the Justice League. It could make them more determined to uphold justice in his memory. They might also become more cautious as they've lost a great strategist.
Batman is a master strategist. He would study the weaknesses of each Justice League member beforehand. For example, he knows that Superman has a weakness to Kryptonite. He would also use his advanced technology and gadgets to even the odds. His bat - suit is equipped with various tools that can be used against different opponents.