Remote Controlled Missile (also called the Nikita) is Snake's Side Special Move. The missile can be controlled with the control stick, but Snake is defenseless until the shield button is pressed. Doing so will end the control over the guided missile, causing it to cease most of its forward movement and drop downwards. The missile will still explode if it hits anything while falling. The missile can change direction randomly if it is hit by rapid attacks like Kirby's and Captain Falcon's Neutral A. When the missile hits its target, Snake will do a quick fist pump. However, when Snake misses he will quickly droop his head in disappointment. The missile does half its normal damage (around 7%) and has less knockback when dropped. It will increase in damage the farther away it is. If you turn the missile, it will travel a smaller distance, due lack of fuel. In the Subspace Emissary, R.O.B. Launchers also fire Remote Controlled Missiles.
Origin
Going back to the first Metal Gear game, the RCM was a weapon that Snake had to obtain in order to destroy a target that was otherwise out of reach. Both in the Metal Gear saga and in Super Smash Brothers Brawl, the RCM is one of the few weapons in Snake's arsenal which is almost completely fictional.