In Pokemon HeartGold and SoulSilver, Larvitar can be caught during the main adventure. You might find it in some of the more rocky or mountainous areas within the game world. Keep your eyes peeled while exploring these terrains, and be ready with your Pokeballs. It may not be super common, but it's definitely obtainable as you play through the main story.
One idea could be that Serena's 'cheating' might be a misunderstanding. Maybe she was seen with another trainer in a compromising position, but in reality, they were just discussing a very important Pokemon training technique that Ash didn't know about at the time.
For Pikachu, it might be very confused. Pikachu is very close to Ash and would sense the change in Ash's mood. It could start to be more protective of Ash and even be a bit hostile towards Serena. This would add an interesting dynamic to the story as Pikachu is usually friendly.
Well, it depends on the context of the light novel. It could have cheats related to leveling up quickly in a game - like scenario within the novel. For example, finding a hidden item that multiplies experience points. Or perhaps cheats for getting rare items or unlocking secret areas. Without reading the novel, it's hard to say exactly what the cheats are.
It could be a mortal man. In Greek mythology, gods sometimes had affairs with mortals. Maybe a particularly handsome and charming mortal catches Hera's eye. He might be a great hero or a simple shepherd with a pure heart.
One common cheat is the health and armor boost. Usually, a specific button combination like up, up, triangle, triangle can give you full health and armor. Another useful cheat is for getting unlimited ammo. It might be something like left, right, square, square. However, using cheats can sometimes affect the game's normal progression and achievements, so use them sparingly.
It could be a mysterious stranger she meets by chance. Maybe at a coffee shop, a guy who strikes up a conversation with her and shows an immediate interest in her life. He could be charming and different from Steve, which draws Catherine to him.
One common cheat is the health and armor cheat. Usually, a specific button combination like up, up, down, down, left, right, left, right, square, and triangle can give you full health and armor. But be careful, using cheats might disable some achievements in the game.
It could be a new character introduced specifically for the fanfiction. Maybe a mysterious stranger who has some ulterior motives and targets Bill because of his relationship with Harry.
In most fanfics, this is often just a fictional and sometimes out - of - character plot device. There's no real evidence within the official Percy Jackson canon for such a thing, but in fan - created stories, it could be based on the author's desire to create drama. However, it goes against the core relationship we know from the original books.