I would have to agree with this.I cleared it with Gladiator Vincent, Samurai Miu, Grand Ranger Cybella, Inquisitor Luthor and Mind Warder Zedd.
The biggest problem is Luthor(boss) who has such a ridiculous status that can one shot your entire backline. Basically, I cycle between stun, blind and sleep. If he manage to resist status aliment, use DEF item and use defend on backline (even that they almost die).
Don't worry about his skill, it only heal 2700 per turn so you can easily outdamaged his heal.
I have to say that it barely worth a reward and 2nd trial is not let anyone die which is next to impossible.
I am currently at -40% on Floor 30 of Tower of Exile.
I cleared it at -32%, and since then I've tried all sorts of combinations to clear the 2nd Trial of "Lose no units"
Technically, my Miu can clear it solo and not die, but because of the stunlocks of the other units, There is zero chance to execute this. The second trial is hell. =/