Since the introduction of the new Raiding with Leashes achievement, I've been farming the old BC raids for new pets. I've only managed to farm up about half, but I'm sure Lady RNG will be kind to me at some point. In my collecting adventures, I've come across a few battle pets that are so irresistibly cute that I could care less about abilities, pet family, or how to obtain them. Lesser Voidcaller definitely falls under that category because of its unique idle animation that summons small spirits.
Lesser Voidcaller drops from High Astromancer Solarian in The Eye, so it's not tough to obtain. Before you engage the boss, be sure to at least kill the two packs patrolling the room, as the casters will use a mind control and force a reset. The entire room will pull with the boss if you don't clear it, but I've never had an issue AoEing everything, even on my squishier priest.
Lesser Voidcaller is of the Magic family and its abilities are as follows: