Here are the monsters that I used for the Labyrinth Boss Guilles in Hell Mode difficulty.
GUILLES:
For me, Guilles is the easiest mini boss to deal with. You just need to make sure that Chloe’s S3 is ready for the next wave and that you have a heal-blocker on your team. Speed-tuning is really important here. You want to make sure that Chloe moves first before the two crystals to protect the team, and then let all the enemies hit you without taking any damage. I used to apply Colleen’s S3 (Fiery Dance) right away, but I noticed that my team kills the wave so fast that by the next wave, Chloe’s S3 is not yet ready. And so, I just use Colleen’s normal attack. Then I use Katarina’s S2 (Soul Reaper) on one of the crystals (preferably the one that isn’t stunned by Shaina). Even though Baleygr’s S3 (Start of Apocalypse) is available, I don’t use it right away. Remember, you need to make sure that Fanatic would be ready for the next wave. Repeat the same process with the 2nd wave.
Boss Battle
Once you reach the mini boss, depending on RNG, Katarina can take out the two crystals and hit the mini boss as well. This would help Baleygr do considerable amount of damage especially with the mini boss defense broken. Make sure to apply Colleen’s S2 (Deadly Dart) to prevent the mini boss from healing after attacking your team. Then it’s just a matter of finishing whatever HP is left from Baleygr’s attack.
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!