Focalor is tough in the colour but he's not hard to beat in the game. Johnny is a known hothead and among the Fantastic Four is the least "thinky". That said, in Johnny's long career, he's a lot more clever than people give him credit for and years of being pushed to use his powers in new ways means he's going to find his way around the demon's water and ice attacks.
I think the second one is super-tough. It's easy to say Iroh with his non-bending fight prowess, his wisdom and his high level bending but Katara, like everyone in Team Avatar, grew fast in their versatility. This is a very even match and I wouldn't be surprised if both parties grew a bit in the conflict. Interestingly, I also think both have abilities neither would want to break out; I don't think Iroh would use his lightning bending simply because it's more likely to do real damage than his fire bending. Meanwhile, Katara is morally opposed to her own knowledge of bloodbending. In the end, I think Iroh would begin the fight conservatively, letting Katara try to exhaust herself while he ducks and weaves until her ability to think on her feet forces him to force him to act. This is where the fight gets more aggressive but it will be an exchange of wits as both parties are trying to force the other somewhere where they can knock them off balance and surprise them. But in the end, I think I have to go with Iroh. Much as I hate the obvious choice, I think Iroh isn't a "set in his ways" fighter, despite his diligence to honing his craft and body, and is quick to adapt. Katara is too but I think Iroh doing that coupled with his strong and dense fundamentals means he's got this in the end, though he'll really need a breather afterwards.
