Magnesium!

Think about what goes into fireworks, welding metals and Epsom salts.

Ive always liked the way Mg works with O2. Its fundamental, Its exothermic, and its self sustaining.
You can do the stoichiometry within your head and even if youre wrong, its easy to correct

Nobody should suggest elements that aren't in the periodic table. We don't want to confuse the guy.