Multi-Form is a technique primarily used by Nappa, Raditz's partner, to increase his offensive capabilities by creating multiple copies of himself. Piccolo, being a Namekian, has his own unique abilities, including:
* Regeneration: Piccolo can heal himself from almost any injury, including being dismembered.
* Special Beam Cannon: Piccolo's signature attack, a powerful energy blast that can pierce through even the toughest defenses.
* Fusion: Piccolo can fuse with other Namekians to increase their power.
During the fight with Raditz, Piccolo utilized his own strength, regeneration, and powerful attacks, including the Special Beam Cannon, to fight Raditz.
It's possible you might be thinking of a different moment in the Dragon Ball Z saga. For example, Piccolo used his "Special Beam Cannon" to try and defeat Raditz, and this attack was incredibly powerful and deadly.