Well, I have some question after playing the Shivering Isle...

What is the relation between these Dark Seducers and Daedric Seducers. I thought they are the same, but... well... Can someone enlight me on this matter?

The Mazken seem to be completely different. The "Dark Seducer" moniker is mentioned in game as being an insult given to them by the golden saints. So I would say they are not the same as the seducers from Daggerfall/Battlespire, and were just named that give them a recognizable name.

Bethesda didn't get too creative with new Daedra in Oblivion. The Aurorans and Knights of Order, which probably aren't really Daedra anyway, are about it.

I thought the name was given to them by mortals.

Eh, maybe it was. I only played through SI once. The point still stands that they bare no resemblance to earlier incarnations of Seducers, in looks or in nature.

dremora look incredibly different than their previous incarnations, pre-mw. Possibly, it was an aesthetic ret-con. Now, as to why they behave differently, the dark seducers of SI are loyal to sheggers, and not mercenaries used by Dagon.

I, also, doubt that these creatures are the same, but for the sake of argument, I'm saying it's possible that they are.

I think the daedric seducer is the mercenary while the dark seducer is truly Sheogorath's minion. But I may be wrong though... who played Battlespire in this forum? I didn't finish it last time. As far as I know both type of seducers exist in the Battlespire.

They'll bite your head off.

The Mazken or the Daedric Seducers? Or both ?

Daggerfall had shapechanging Daedra Seducers.
Battlespire, for technical reasons, couldn't keep the shapechanging animation. (They went with hi-res sprites and it took too much video memory or something to store two sets of animation + the transformation animation for just one sprite set.) So, although they were still supposed to be capable to shapechange, throughout the game, they just don't happen to do it. In Battlespire, "Daedra Seducer" is used to designate those that are always in human shape, and "Dark Seducer" for those who are always in demon shape. Still in Battlespire, the Dark Seducers are Dagon's servants. Since Dagon is the Prince of Destruction, Brutality, and Being Not Subtle or sixy At All, his servants are in the shape that is the most pleasing to him: brutal and not subtle at all. The human-shaped Daedra Seducers are their own self, and give a greater importance to looking sixy and human-like.

Are the Daggerfall/Battlespire Seducers the same as the Mazken? Maybe. We could just say that Dark Seducers are Seducers in the employ of a Daedric Prince. Sheogorath is not necessarily big on having feral-looking servants with green-and-red wings, so Sheggy's Seducers are as we know them.

Were the Seducers in Battlespire Sheogorath's?

Or just freelance Daedra?

I believe that there is at least a partial explanation http://www.imperial-library.info/interviews/si_interview.shtml.

Yes, here;

Okay, so now, why does Haskill hate Mehrunes?

Thanks for the link!

because he is sheogoraths butler.

I'm speculating here, but maybe Mehrunes Dagon lacks subtlety; he would appear to some of the Princes such as Sheogorath as a thug who wants to destroy the Mundus, while they prefer mortals to exist as toys.

Aren't they all freelance daedra?