"Here's a thing you need to kill for a useful ability! Oh, and he's got two friends, but you have to kill him first. No, they're much weaker than him, hilariously so. They'll paralyze you for him to kill though. And they occasionally grab you and explode. What? Yes that counts as killing them before he's dead!"
FUCK the Head Case VR mission. Finally broke down and changed the difficulty to Easy and threw Barret in by himself. Seriously, you have to kill a Mindflayer, but he's got two Varghadpolis and you fail the mission if you don't kill the Mindflayer first. Varghadpolis, or at least this particular variety, has a shitty HP pool (especially compared to the BOSS enemy) because how you're supposed to handle them is to kill them first- they have a countdown, after which they will spam an AOE move that paralyzes you. And, as mentioned, occasionally they will self-destruct, fucking you over anyway. I'm pretty sure the mission is supposed to be done solo, because AI teammates will fuck you faster than anything.
Specific strategy: Binding(sleep) Materia + Magnify so you can hit all three. Do NOT sleep the Varghadpolis right away or whenever you can, use it to SEPARATE them from the Mindflayer whenever you have a Limit Break or other ability built up so you don't accidentally kill them when you hit the Mindflayer, because you have limited MP and enemies build up resistances to status effects after they're used. The Maloboro Orb is recommended to extend that sleep and make the paralysis last a lot less time if it catches you. Barret's good because he's got a lot of HP and Steelskin to defend himself, give him a healing materia to make up the difference. Try to use Maximum Fury instead of Focused shot because it's not an AOE. Bonus Rounds doesn't have a time limit, so pop that if you have a spare ATB.
And watch the teleport because the Mindflayer will pop out of existence sometimes when you use a strong attack, making you automatically lock onto one of the little shits instead.