: So I don't (and probably never will) own an XBO, so I watched all of the
: cutscenes here . Which let me to a few questions: 1. Master Chief can't
: understand Regret's hologram without Cortana translating it. So how can he
: understand Mercy?

It could be explained that Cortana had gotten enough of Regret's speeches along the journey to be able to derive a translation of the Prophet's language and then upload that to the Chief's software in the armor (or neural implant). So Mercy may have still been speaking in his own language but the Chief heard it translated into English.

: 2. Was 2401 Penitent Tangent compromised, or did he say all of the perfect
: lines of his own volition?

This one kind of flops. A misaprehension on 343i's part made them think 2401 PT's eye color was red, where the model asset and textures indicate he was identical in every way to Guilty Spark, including the blue eye, however he had a 'drape' of Flood infection texture over the model making the eye appear reddish, but not actually red. This would indicate that 2401 PT was in fact infected technology. He still spoke of his own volition as did Regret, even though both were hopelessly captured. Also, despite the popular opinion, I would say that 2401 PT was not answering the regular communiques because containment had been breached and he had been captured, rather than he'd gone rampant and left the facility to decay on its own.

: 3. The Halos are put on standby activation, which 343GS says means the Halos
: can now be fired from the Ark. So otherwise, they can't be fired from
: the Ark? That seems like terrible contingency planning. (Also, in
: Silentium, the IsoDidact does fire them that way.)

I think all he meant by that was that now the the array was in standby mode, only the Ark could activate them, but if they'd been online normally, the Ark could still have done it anytime.