For this dungeon you will need at least one character able to heal, even very weakly, to make the Royal Pingwin vulnerable.
If this is your first time doing this dungeon, you will automatically complete the quest "Les Joyeux de la couronne", which is required to use the Frigostian transport.
In some rooms of the dungeon you will find Apewicubes (ice cubes with an octopus inside). Use them and you'll get a gift ^^
Once at the bottom, just head left until you reach Waldos. Talk to him and give him the key, or use your keychain to enter the dungeon.
Monsters
Mama Pingwin
Mamansot
Lvl 122 to 134
Pingwinkle
Timansot
Lvl 111 to 119
Pingwobble
Mansobèse
Lvl 116 to 128
Shaman Pingwin
Shamansot
Lvl 125 to 137
Kung-Fu Pingwin
Fu Mansot
Lvl 131 to 143
Rooms
Room 1
Room 2
Room 3
Boss
Royal Pingwin β
Mansot Royal
Lvl 162
Dungeon mechanics
How to make the Royal Pingwin vulnerable:
All you have to do is heal one of your allies in melee with the Royal Pingwin. It then becomes vulnerable for 6 turns. After that, you have to repeat the maneuver. This system does not work if you heal a summon in melee with the Boss.
Finding the right tactic isn't easy; it depends a lot on your team. Obviously, killing the Boss first is easier if you can handle the damage dealt by the other monsters, because a Royal Pingwin left after the map is cleared means a lot of HP, MP and damage ^^
Maybe the ideal solution is in between: kill the Mama Pingwin to avoid the summons, then move on to the Boss. It's up to you to find the right technique ;)
Achievements
End of the dungeon
You can now access Alma's Cradle, the next area of Frigost