A powerful and greedy landowner could be the antagonist. If Shrignold and Tony are trying to protect a piece of land or a natural resource, this landowner would be against them. He would use his wealth and influence to try and stop them from achieving their goals.
A possible plot could be that they both have a common goal. For example, they are both trying to solve the mystery of a disappearing stream. Shrignold with his knowledge of the natural elements and Tony with his sharp observational skills work together. Along the way, they have some disagreements but soon realize that by combining their strengths, they can get closer to the solution.
Maybe it's an old clock - maker named Mr. Grimsby. He has a dark past related to a cursed clock he once made. When he hears about Tony's interest in clocks, he fears that Tony will discover his secret. So he tries to stop Tony from delving deeper into the world of clocks by causing problems in Tony's life, like getting him fired from his job at the local clock shop.
It could be a local Siberian warlord who sees Tony as a threat to his power. Maybe Tony's presence in Siberia disrupts the warlord's plans for the region, so he decides to eliminate him.
It could be a new villain that we haven't seen in the original Marvel universe. This villain might be able to manipulate Natasha's emotions and loyalty, making her betray Tony. For example, a powerful sorcerer who uses dark magic to control her.
Maybe an old enemy from their time on Earth who somehow managed to get into heaven. This enemy could hold a grudge against both of them and wants to take revenge. They might use their knowledge of Tony and Natasha's past weaknesses to try and defeat them in heaven, where the rules are different from Earth.
It could be someone from Stark Industries who doesn't like the idea of Peter inheriting something. Maybe a rival within the company who sees Peter as an inexperienced kid and wants to take whatever Tony left for Peter for themselves.
It could be a scientist who is jealous of Tony's inventions. He creates a device that causes the hiccups as a way to disrupt Tony and Peter. His goal might be to steal Tony's technology while they are distracted by the hiccup problem.
It could be the sister herself in a sense. Her over - the - top fan behavior might cause so many problems that she becomes like an antagonist to the normal, smooth - running of the Stark family and the superhero world around them.
It could be a new villain who has the ability to manipulate minds. This villain could make Steve believe that he is a danger to Tony and Peter, causing him to leave. For instance, the villain might implant false memories or thoughts in Steve's head, making him think that his actions might accidentally harm them in the future.
It could be a future version of himself that has become corrupted by power. He sees this future self causing chaos and destruction, and has to find a way to stop his own dark path. Maybe it's a result of his technology getting out of control and warping his mind.