Guided Robo Beam
From SmashWiki, the Super Smash Bros. wiki
When activated, R.O.B. transforms into a laser cannon and fires a series of small lasers that home in on opponents that are close enough to him. He then unleashes a green laser that can be angled up or down. After a couple of seconds the laser grows larger, about the size of Samus' Zero Laser, and ends with a powerful blast.