Well, they might be shocked at the turn of events in Volume 3. For example, Cinder could be secretly pleased with how her plans are progressing while outwardly showing a calm facade. Roman might be frustrated if things don't go as he expected in the fanfiction, like if his heists are thwarted more easily than in the original story.
In the Volume 3 fanfiction, the villains' reactions could vary greatly. Some might be more vengeful. Neo, for instance, could be extremely angry if her partner Roman is in trouble. She might take more risks to save him or seek revenge on those who caused his problems. Adam could be more calculating, seeing the chaos in Volume 3 as an opportunity to further his own goals of faunus supremacy.
The RWBY villains in Volume 3 fanfiction would have diverse reactions. Salem, as the main overarching villain, might be either satisfied or impatient depending on how her minions are performing. If they are making progress towards her goals, she would be content. But if they are making mistakes or being too slow, she could become quite impatient and start to micromanage the situation more. Other villains like Torchwick might be more concerned with their own survival and personal gain in the events of this fan - made Volume 3 scenario.
They might get angry if the fanfiction portrays them in a way they don't like. For example, if they are made to look weak or foolish.
Ruby would likely have a big smile on her face. She's always positive and would be happy to see the creativity of the fans. So she'd probably be all for it.
Perhaps they would show excitement when seeing their favorite characters in intense battles as depicted in the 'rwby reacts deadliest warrior fanfiction'. Since the 'Deadliest Warrior' concept usually involves some really cool and over - the - top fight scenes. And if the fanfiction is well - written, it can bring out a lot of emotions from the RWBY characters who are reacting to it.
Well, Naruto might be really confused at first. RWBY has a very different world setting compared to his own ninja world. He'd probably be intrigued by the unique characters and their powers in RWBY. For example, the use of Dust in RWBY might seem really strange to him as he's used to chakra-based abilities.
They might be surprised by the complex and often dark themes in Warhammer fanfiction. RWBY characters are used to their own universe's rules and aesthetics, so the gritty and elaborate world of Warhammer could be a shock.
They might be shocked. In many cases, when a character like Jaune is betrayed in fanfiction, the RWBY characters could initially show disbelief as they've come to know him. It would disrupt their view of the group dynamic.
They might be shocked by the different powers. For example, RWBY characters are used to their own semblances, and seeing Naruto's jutsus like the Rasengan would be quite a surprise.
Well, they might be shocked. In the RWBY universe, the concept of betrayal is quite serious. If it's a Rose character being betrayed, the team could first show disbelief. They trust their comrades deeply, so this would be a huge blow to their morale.
A power - hungry villain like Cinder Fall might not care much for Red vs Blue fanfiction. She is so focused on her own goals of power and domination in RWBY that she would likely see the fanfiction as a distraction from her important business.