I'm not sure if Galyxx is a boss killer, but it isn't a minion-killer; no AoE abilities whatsoever. It's built to ambush targets, pin them down with Dimensional Anchor, then either Sleep them or Ability-damage them into incapacitation. Definitely at its best 1v1, but bosses tend to come with minions, and Galyxx is pretty fragile if you can pin down its location and bombard it with attacks.