Complex sentence: A Blue Koopa shell is also a type of armor in "New Super Mario Bros.", giving Mario the ability to retreat into the shell and launch himself like any other Koopa shell.
Split into simpler sentences: A blue Koopa shell is also a power-up in "New Super Mario Bros.", in which Mario wears the shell just like a Koopa. It gives Mario the ability to retreat into the shell and launch himself like any other Koopa shell.