Vagra II is a barren planet where the malevolent being Armus was abandoned and where Tasha Yar was killed.
Vagra II is a desolate world in Skin of Evil. A shuttle carrying Deanna Troi crashed there, and when an away team beamed down to rescue her, they found a pool of tar-like matter that called itself Armus. The being was the cast-off evil of an ancient race, left behind on the planet.
Armus killed Tasha Yar when she tried to reach the shuttle, then tormented the crew for its own amusement. Picard confronted it and kept it distracted while Troi was rescued, and the Enterprise left Armus alone on Vagra II.