Fought Tetra and Diabolos earlier today.
I cleared Tetra Slypheed with a team of Wilhelm, Basch, CG Fina, CG Nichol, Kid Rydia, and a Friend 7* Dark Fina to chain quake. Wilhelm was a wall. Basch had 150% of fire and wind but still took damage occasionally. The fight was without issue until 40% where Wilhelm got snorted. I had two turns sub 40% where Fina's LB reraise kept a couple people up.
For Diabolos, I took Wilhelm, Basch, Ayaka, Orlandeu, and a friend Orlandeau. I lost, I'm going to try again tomorrow and swap in Warrior of Light and Mystea. Wilhelm with 15.5k HP and 1.1k defense still died a couple of times, so swapping in WoL who still has all my evasion gear will help there. Although that wasn't really the problem as keeping re-raise on him mitigated that fairly well. My issue was the lack of stop immunity, Mystea was on an expedition, so I just rolled with Ayaka and her stop cure; which was not as good. It actually worked fairly well until 40% where everyone the aoe stop ended much worse than the previous for some reason. The surprising thing was that my Orlandeau(6*) and the friend Orlandeau(7*) didn't do as much damage as I would've thought. Only about 6-7% in a chain without Basch's defense break; but I should be fine with any dps as long as I have the stop resist.