Yep, magic. I did a worldbuilding post on magic before (blog link) but here is another one with a slightly different focus. There are many ways to use magic within a story, in particular in speculative fiction. However, there have to be limits because if magic can do anything, if the main character can do anything then it becomes boring.
Me and a friend had a disagreeance on this topic. He does a lot of RPG stuff online and would tell me about some of his characters. Bascially they were all powerful and could always get what they wanted but for me that was boring. I'd rather see a character who has high powers in magic be someone who struggles, not someone who barely has to make an effort to get anything done. There needs to a be a challenge, the character needs to struggle for the reader to really feel and empathize with them.
Also, it helps to have some sort of complication to the magic. In many fantasy stories, the use of magic draws off the character's energy so they become tired after use. But stories try to vary the consequences of magic. In Stardust by Neil Gaiman (I believe, haven't read but saw the movie) when the women use magic it ages them. In Wheel of Time series by Robert Jordan for the women the use of magic wears of them but for men it eventually drives them insane. In some worlds the use of magic is forbidden with harsh consequences if discovered.
I have a few characters in my many novels who are very powerful in their worlds. Noah is the most powerful mutant with his controlling energy in ways that could come out in like atomic bomb level proportions. Daemahrath is an elf in the epic fantasy story who not only has magic abilities that most don't do anymore in the world but also is a skilled fighter.
Noah might be powerful but he hates it. He doesn't want to be a mutant and struggles through the series with his abilities and the fear of being used as a weapon. His hard time with the nature of his strength helps because it causes him to struggle. His emotions affect his abilities though.
Daemahrath on the other hand, has to hide his abilities and struggles in a different way. In part, he is balanced by the other elf main character, Feynethom who not only does not know how to use any type of magic but also is a terrible fighter. But also, he's well aware of his strength and has to work hard to keep himself under control. Using it does wear on the character's energy requiring rest after so much but I'm also thinking of having the magic connected to carnal urges that he has to struggle to contain as well.
What magic does your character use?
Are there consequences?
Do you find the all powerful character boring?