There are a lot of interesting pieces of dialogue in the video above.  I've found that this page offers the most accurate assessment of the dialogue.

We see a lot of really surprising and different grammatical things here.  Compound words and possessive suffixes are used heavily: "suleyksejun", "losei", etc.  We also see "se" being used a lot.  So far we've seen it used to make compound words like "suleyksejun", but here's it's being used as a suffix.  I can't quite determine what purpose it's serving though.  What makes "Ful, losei Dovahkiin" different from "Ful, lo Dovahkiin"?

Thoughts?  Once we figure this out, I foresee an advanced Dragon Language lesson covering all of these grammatical intricacies.

When I saw the "losei" I figured it was a rare use of verb tense.

maybe it's something equivalent to "thou art"? heh.

"Losei" is supposedly based off of "lo" (deceive) and means "false".  It is "lo" with "se", and the possessive suffix "-i" to make "losei dovahkiin", "my false dragonborn".

hot damn. 

so where does the "se" part of that come in from? is it just being used as that conjunctive to separate the syllables lo, i?

hmm...

If the purpose is to separate "lo" and "i", it doesn't really do much since "se" ends with a vowel too.  The other example we have is "Ulse", which doesn't have a possessive suffix like "-i".  I liked your earlier idea that perhaps it stands for "for", "bound to dovah for eternity", but that doesn't quite fit with "ful, losei dovahkiin", "so, for deceive dragonborn".  At least, not in any way that makes sense to me.

To note is that "ul" is a noun and "lo" is a verb, so maybe it means different things when attached to one or the other?  "For" when attached to nouns, but when attached to verbs...could it possibly be like "-ing"?  "My deceiving dragonborn" (my false dragonborn).

Losei... 

Lo = deceive

-se = -ive?

lose = deceptive? 

"having the capacity to deceive"

receptive, secretive, responsive

similar to -aal but maybe that modifies nouns and -se modifies verbs?

because we have -von (-ing) for the verb-to-participle conversion.

What if Ulse meant "eternal"?

Having the capacity of eternity? (for lack of better wording)

Though that would be Ulaal...

It's either "for eternity" or "eternally".

Here's the wiktionary entry for the suffix "-ive".

An adjective suffix signifying relating or belonging to, of the nature of, tending to; as affirmative, active, conclusive, corrective, diminutive.

Doesn't that certainly sound like "se", meaning "of/belonging to"?

very interesting. so it's just another use for (and slightly tweaked definition of) "se"

Yup, as a suffix to form adjectives (deceptive/false), while the possibility of it representing "for" is also there.