Unavoidable death mechanics should not be a thing in FFXIV :(

[TaleraRistain]

Edit: I still interpret the description as being Cid's Crush Weapon. If Vyrerus is right and they actually meant Agrius's ruination that makes even less sense. That attack is both avoidable(do the shield mech/dont stack on the person targetted), and doesnt even deal lethal damage unless you have a few vuln stacks.

I was thinking Cid's Crush Weapon or possibly the tethers, which you're supposed to share.