What's the coolest weapon or powerup in any video game?

As the world's only interactive art form, the medium of that interaction, the locus of engagement, has always been central in video games. Hence we see why 'has cool guns' and its less violent cousin 'lets you do cool stuff' have always been pushed as selling points for video games, and in this bounty, we're going to settle the coolest.

Tell us what you consider to be the coolest, best, or most memorable weapons, guns, or powerups (things like Duke Nukem's jetpack or Doom's Berserk mode) in any video game. Anything that shifts your interaction with the world a few notches up the 'cool' meter is eligible. Tell us what it is and why it's so awesome/enjoyable!

Feeling inspired? Create your own weapon or powerup!