They could be from a fight with a powerful magical being. Maybe Loki tried to steal a powerful artifact from a wizard or a sorcerer, and in the process, he got injured and the scars remained.
Timely Comics isn't in the public domain. Their characters and stories have ongoing copyright protection. This means you can't use them freely without permission.
Thor could also become very angry. Not at Loki, but at whatever or whoever caused those scars. He might vow to avenge Loki and seek out those responsible. For example, if the scars were from a battle with a particular enemy, Thor would be determined to confront that foe.
Timely Comics was moderately popular. It had a decent collection and attracted a fair number of customers, but it wasn't the most renowned in the area.
I'm not sure who Victor Marx specifically is in this story without more details. He could be an ordinary person with an extraordinary story, or he might be someone well - known in a particular area.
I'm not sure specifically what 'Timely Errors' refers to in a Harry Potter fanfic without more context. It could be the name of a unique plot device, like a spell that goes wrong at just the right or wrong time. Maybe it's about mistakes characters make that end up having significant consequences in a timely manner within the story.