Special Weapon for Side Scrolling shooting game.

Hi, I have a project that is a side scrolling space shooter game, I’m having trouble on how do I make a special weapon for my spaceship, like for example when the bar is full, the user can now use the special weapon by pressing control button…something like that…Does anybody know how to do the special weapon for side scrolling shooting game?

What code do you have so far?

How about a key combo - like an old school arcade?