|This article is in need of content, please consider adding to it.|
Stheno has the abililty to absorb strength from the other monsters in the dungeon. When you first attack Stheno, every other monster will disappear and be converted into physical and magic resist (4% per absorbed monster). This also includes Revenants, but not monsters that reside in subdungeons, nor plants. There is also another boss chosen randomly. This second boss is not removed from play when Stheno absorbs monsters, but seeing as you are capable of using level-up catapults against this second boss it almost always preferable to leave Stheno for last.
Since Stheno cannot absorb monsters in subdungeons, it is possible to get a level-up anyways by preparing the Smuggler's Den and needing exactly 1 or 2 XP to level up. However, manipulating your experience so precisely will force you to leave some monsters alive for her to absorb, which may do more harm than it's worth. Goblin is a more reliable way of getting a level-up against her.