On the UESP, http://uesp.net/wiki/Lore:Boethia, Boethia is described as allied with the Temple of Stendarr. I'm confused, seeing as Stendarr is "good," the god of mercy, while Boethia is "bad," the god of deceit, assassination, etc. Why would Stendarr ever ally himself with Boethia?

Firstly, that's old lore and not necessarily true anymore.

Secondly, Boethia isn't necessarily bad. He/She wants mortals to be strong and independent (this is especially telling in the Molag Bal shrine quest ).

Weellll, you see, the two of them used to be huge lovers. I means, they were making Sanguine's orgies look like a church. But, Boethiah dumped Stendarr one day, as Boethiah was going through a bit of a crisis, and now Stendarr has become a very bitter ex-lover. This is also why all of his vigilant to take out his anger on all daedra, daedric worshippers, and anyone affected by a prince.

It's quite a sad story, really.

Fixed

EDIT: BLeh, duh.

If you read closely, you'll notice how some of the Divines and some of the Daedric princes are quite similar.

Stendarr is not just mercy, he's also righteous might. He's a patron of mighty kings, lords, people who choose to exercise power. Boethiah shares his audience.

I think there are two points of note in this.

First, Boethia, while manipulative, fickle and generaly unpleasent likes to test mortals to become the best they can. Theres nothing wrong with helping others so long as you don't let it compromise your strengths. Boethia can also encourage mercy, as someone you save one day can be someone to be used another.

Second, if you think about the Vigilents of Stendar, they are a religious order. more specificly, they are a religious order which, unlike Daedric Cults, does not have actual contact with their god. Stendar and Boethia could still be tenious allies on the higher/lower planes, but the church has no way of knowing, because Stendar doesn't directly communicate with them. What the Church says, and what is actually going on, are probably quite different.

Stendarr is the true god of power, because whoever heard of a victim having mercy?

This. Stendarr represents the ultimate expression of personal power: the ability to take a life, and the will to choose not to.

Stendarr and Boethiah, upon further reflection, seem to be polar opposites. Stendarr is the deification of restraint, and Boethiah that of ruthlessness. Note also that it's Stuhn's mirror who killed Tsun. We need to think about this more, it could hold some useful information on the Mythic, especially in conjunction with that On Boethiah's Summoning Day thing. Didn't the first letter mention Stendarr's star being prominent?

...your churches don't hold orgies?

btw, this thread has brought up some really great points about Boethiah and Stendarr, and the nature of mercy. Good stuff.

Simpsons reference.

ah, damn my pop cultural ignorance.