Injector is a droid sent by Emerald to fill a vulnerable spot with dark energy. Her arms are made of needles and she can inject people with them to make them sick. She appeared in Sailor Moon R Episode 31, No Thanks, Nurse Venus!
Emerald placed a Dark Wedge in a hospital, one of the vulnerable spots of Tokyo, and summoned Injector to fill the area with dark energy by making everyone sick with the flu except Mina and Rini. When Mina and Rini came over to get medicine, they discovered what Emerald and Injector were up to, and fought them. Injector pinned Sailor Venus to a wall with needles and went after Rini, but Tuxedo Mask shattered one of her needles, and then the other Sailor Scouts, having recovered from their flu, arrived to fight Injector. Emerald ran off. Sailor Moon destroyed Injector with her scepter (once again, as was the case ever since her fight with Rubeus, she says "Activation" instead of "Elimination").