Current State of End-Game Contents - A Blog Post from A Japanese Player

[LunaHoshino]

So, the Final Coil bosses get stronger when people die? They do different things? They can be beaten in more then just one way? You don't all wipe if you do something wrong?

In T10, if someone dies or you mess up a mechanic, the boss gets a stack that increases the damage done by the unavoidable AoE that he does at the end of every add phase. The boss also gains stacks during the add phase, so if you don't kill the adds fast enough, you can end up with a wipe.

The final phase has three different sets of mechanics that happen at random, each one requiring a different method of handling them. There's a loose pattern in the sense that you won't get two Wild Charge combos in a row, but other than that, there's no set rotation for them.

I have yet to try T11 for myself, but the tethers in that fight are also random. How you deal with them depends on what tether combos you get.