The Marauders' presence would likely change the dynamic completely. They could offer advice to Harry based on their own experiences. For instance, James could share how he won over Lily, which might influence Harry's approach to Ginny. Also, their very existence in the fanfiction world could introduce new plotlines. Maybe they could help Harry and Ginny solve some problems that they couldn't have solved on their own. And their different personalities would also have an impact. Sirius' boldness and Remus' wisdom would both play a part in shaping the story.
The marauders' presence in 1995 would likely disrupt the normal flow of things. They could influence the relationships between the characters. For example, they might become friends with the Weasley family and introduce some new pranks or ideas to them. Their knowledge of the past could also help in dealing with Voldemort, but it could also create confusion as they may not fully understand the current situation. And they may have some conflicts with certain characters who don't trust their sudden appearance.
If their plan was to protect Harry before he even got to Hogwarts, it could change a lot. For instance, if they managed to defeat or at least keep Voldemort at bay, Harry might grow up in a very different world. He could have a normal childhood without the threat of the Dark Lord constantly looming over him.
If Harry and Ginny meet the Marauders in fanfiction, it would be a moment full of emotions. Harry has always longed to know more about his father, and this would be his chance. The Marauders, on seeing Harry, might see a lot of James in him. Ginny would add a different dynamic to the group. She could be the voice of reason at times. Together, they could create new memories. For example, they might team up to play a prank on Snape's memory or something, which would be both funny and a way to pay homage to the Marauders' legacy.
His presence could make Harry more protective. Harry might be more cautious in his adventures, not wanting to put his little brother in danger. For example, when dealing with the Marauder's Map, he might be more hesitant to use it if he thinks it could expose his brother to trouble. Also, his friends like Ron and Hermione would have to adjust to having a younger, perhaps more inexperienced, person around. They might feel responsible for him as well.
The dragon's presence could have a significant impact on Hogwarts. For starters, it would change the security measures. The school would need to figure out how to keep the dragon safe and also protect the students from it. There might be new spells and enchantments put in place. Also, the dragon could become a part of some classes, like Care of Magical Creatures. Students would learn about its unique abilities and behaviors.
The overall mood would likely be quite tense. Since Harry has a lot of bad memories associated with his uncle, seeing his boggart as his uncle would bring back those negative feelings. It would create an atmosphere of unease and fear every time the boggart appears in the story.
Ginny would likely be protective. She loves Harry and knows about his difficult past with the Dursleys. So she would probably stand up for him right away, not tolerating any of their mean remarks.
His relationships would likely be in turmoil. His friends might notice a change in Harry and be confused. Loki could make Harry act distant or say strange things to Ron and Hermione, causing them to worry. And his relationship with Ginny might also be affected as Loki might make Harry act in ways that Ginny doesn't understand.
It could boost his confidence. Knowing that the Weasleys are there watching him, Harry might feel more determined to do well.
It could change the story by introducing new skills. For example, if she knows martial arts from the modern world, she could use it against Titans in a different way than the characters in the original story.