Here are the monsters that I used for the Labyrinth Boss Kotos in Hell Mode difficulty.
KOTOS:
Kotos is a very annoying mini boss. The dots would really hurt your team if you don’t have any cleanser with you. My first team initially has my main Lulu and Friends that uses violent rune. However, procc’ing out of the immunity buff is very problematic. Not to mention the attacks that she deals are negligible. I keep getting killed by the dots. So I opted to use my 2nd Lulu and Friends that uses revenge runes. It turned out really well.
Boss battle
The rune order for me would be revenge > violent > will > rage. I prefer to deal with the revenge first because most of my units uses violent runes. You don’t want Kotos revenging on your monster’s measly damage. My team can pretty much tank the violent hits as long as Woosa has his shield buff and I don’t really need to worry about the rage rune since I have two units that give immunity. So I won’t get insta-killed by the mini boss.
Video
Team composition
Here are my team for the other bosses:
I wish you luck in your quest to finish hell mode on all the lab bosses, summoners!