The Hivemind is replaced by the Aberrant Hivemind on Challenge Level 1 and above. The Aberrant Hivemind has more health and damage than its lesser sibling, but otherwise behaves similarly to it.
Your best arena is the beginning of the stage so summon it near the spawn. Wait for it to arrive and when it does, use every time it pauses as an opportunity to attack. The Hive Mind will shoot 3 bullets (4 Damage each) and then move. The best solution is to use a Tech character with Gadget Turrets or Plasma Grenades to take advantage of its stops and be more mobile. Another good way of defeating it is to use an enforcer with ringabolts axe, as one projectiles can hit it 3-5 times and you can still stay in safety while defeating it fairly quickly depending on your strength stat.