Trials of Decimation tutorial video.
The embedded video below jumps straight to the boss wave of the last level. The bosses are Oberon, Ulmer and Baltthazar. I had few choices among my 4-star classic Wizards and Fighters so I ended up taking 3 Kirils, Boldtusk and Hu Tao. 4 healers and a 4-star yellow tank. It is possible to beat this quest with only regular heroes. You just have to count on tile damage and your healers since there are no healers among the bosses. At least I didn’t need to burn any revive scrolls on this quest.
If you have any high powered Wizards you should definitely take them instead, they will make your quest so much easier. If you have even a Proteus from Atlantis, the final boss wave becomes a practical cakewalk when you use mana potions to charge up Proteus.