Lightsaber Clone is a clone from Base 327. He has only appeared in two episodes, most notably in the New Years' episode. On Christmas Day, the Lightsaber Clone found General Grievous's lightsabers in the pile of remains the Janitor threw out after Grievious's battle with Santa Claus. When he returns and shows them to everyone else, he proclaims that since he found them, one of them should be his. The other three lightsabers go to The Commander, Rico, and the Excited Clone. The Commander bans the Janitor from having a lightsaber because he was the one that threw them out.
The Lightsaber Clone was not seen for a long time afterwards, until the Mystery at Base 327 series, where in the second episode it is revealed that ARF has stolen The Commander's lightsaber. When The Commander tracks ARF down, the Lightsaber Clone offers The Commander his lightsaber so that he can duel with ARF. Upon receiving the lightsaber, The Commander notices that he "forgot [the Lightsaber Clone] existed," to which the Lightsaber Clone responds, "Me too..."
The Lightsaber Clone was probably forgotten about by the creators of Base 327 because he's quite indistinguishable. He wears phase 2 clone trooper armor, which many of minor characters/extras wear as well. In fact, because of this, he can easily be mistaken for the New Guy, who wears the exact same armor, but has a main role in the series and is voiced by a different actor. The only real physical difference that separates the Lightsaber Clone from others is that he has a blue lightsaber. The only other person in the base that has a blue lightsaber as well is the Excited Clone, who wears phase 1 armor and can be recognized by his extreme shaking and hyperactivity.