Just lost another char (an Oni Fire Elementalist) against Duvessa. Managed to separate the 2, took out Dowan without much trouble and Duvessa wasn’t even aware of it. She still gets permanent berserk the moment she sees you. Giving her berserk the moment she sees dead Dowan makes sense to me and if that were the trigger that would create some interesting tactical opportunities.
As is if you kill Dowan first, you just have to leave the level until you are much stronger. 36 HP, permanent berserk, generally a melee weapon for 20+ damage per turn is just nothing any char on D5 can take. So this feels like a trap, kill Dowan and your char is screwed unless you know about this beforehand and quickly find some stairs.
I feel as is it is set up as a trap for the player.
Compare to Siegmund, who also kills plenty of low level chars. But if you read his description it should be fairly clear that he is super dangerous and most chars should try to avoid him when they first see him.
When you encounter Dowan and Duvessa and it looks like the key point is that they are twins and that they can buff each other. So that suggests the strategy should be to separate them so you can take them on one at a time.
But the mutual buffing is mostly irrelevant, once you take out one the other one will be perma buffed and in a stronger way than they can buff each other. So when you encounter them you need to ask yourself whether you can take on either one on their own perma buffed. The whole twin business is just a decoy. And for most chars the answer will be no.
So if you know about this, you just avoid them completely but the monster description leads you to a totally different approach. To add insult to injury both will become hasted when buffed making it close to impossible to run away from them for a char on D4.
It is a question of what the intended player experience is.
If you want ‘here is a monster most players can’t take on’ that fine (see Siegmund) but that should be clear from the monster description (see Siegmund again).
If on the other hand you want ‘here is a pair of monsters, harmless on their own but dangerous together’ (which is much more interesting to me than another Siegmund) than after you kill one the other one should be mostly a push over.