I don't know if it counts, but if I had enough radiation protection, I'd say Urayne from Pokemon Uranium just after you defeat it for the last time and are given it alongside the core that allows it to essentially live forever. Though, I assume by that point you wouldn't need radiation protection considering you never see the player character pull out the advanced radiation suit when you gain access to use him in battle.

Don't know if doing something like the one time Curie did that quantum leap would count as a magical power, but imagine how cool it'd be to be able to teleport anywhere (depending on if quantum leap has no limits on distance) for free.

Also, I'm sure this would count as a magical power, but unlimited nuclear energy for free would be amazing.