Hmm, well thanks for actually bothering to check this out.
Well, the first thing to worry about is whether these are meant to be sentences. Copulaless and many suffixes having multiple uses, in Dothraki most of everything can be read as a sentence. So Khal shekhi driv. would mean something like King of the sun was dead. But maybe you were aiming for king of the dead sun? Then the adjective driv would get an -a suffix, to mark that the word it modifies, shekhi is not in nominative case.
The genitive construct, khal shekhi is, at least at first glance, a bit iffy, but I think it should work. There are probably even examples of similar use. The sun is not an owner of the king, quite the other way around, so this is a bit extended use of genitive. The most obvious alternative would be to use ablative. One or another is probably the right way and the other is a bit off.
I wanted to say "The lord of the dead sun." So I'm assuming "khal shekhi driva" would be correct. It's naught but a mere title, and not a sentence.
The magician of the wasteland of dragons. The genitive constructs probably works in this as well, though I would not bet heavily on that. As Dothraki aren't too keen on marking plurals or making indefinite/definite distiction, this could mean eg. a magician of the wastelands of the dragon, but that's as it should be, IMHO.
I know it's nothing but semantics, but I was going for warlock here. Sounds more menacing. But yea, it doesn't really matter whether it's a singular dragon or plural.
I'm guessing this is to eat a rotting corpse. As far as I can think, khadokh will never get an -e suffix. Inanimate nouns that in nominative end in a vowel sometimes get an -e suffix in accusative, but inanimate nouns ending in a consonant (or animate nouns of any kind, for that matter) never do. On the other hand, rikh should again mark the non-nominative case of the word it modifies with an -a suffix.
Hmm, my bad. I don't know why I even bothered modifying "khadokh," as it's already the bare stem, I assume. I'm still not sure on how to modify the adjective to fit the cases, though. But uhh, why an -a suffix? I presume it's an universal inanimate-accusative-adjective modifier.
I slew a person ... prophecy? I don't quite understand, how that assikhqoyisir is meant to figure to the sentence. Anha drozh vojes is simple enough and should work fine. I translated voj as a person there, but it's much more everyday word than that, so a man is probably closer to it's tone.
I slew the prophet. Since there is no word for prophet, I've "coined" my own, "voj assikhqoyisiri," which means
man of prophecy, as you most likely know. Again, I've did a small mistake and forgot to add the genitive suffix in the title. So I take it that "Anha drozh vojes assikhqoyisiri" works?
To ride the pale mare. Once again the adjective should have an -a. The vocab does not list the animacy of lame, but animate is pretty safe guess. Messhihven is a bizarre adjective to be used of a horse. It's a word for human skin colour and literally means "white horse -like". Perhaps it's appropriately bizarre, though. I have only an inkling of the nuances of the different to ride words, but I think vidrogerat might be pretty good choise.
Yes, the adjective marker. But from what I've gathered on the dictionary, messhihven is pale-skinned, nothing more is written. Perhaps it speaks of humans, but I don't really know. With this title I was going for the bloody flux idiom the Ghiscari (I think) use, so I'm assuming the Dothraki have on of their own.
We went to the land of gods. Kisha is plural, so elat should be in past plural: esh.
I'm pretty sure mra does not work there. Mra is much more inside than English in or even into; she is the "neutral" Dothraki preposition, which often works even where English use in. Here, though, no preposition is needed, IMO.
Oh, whatthehell. It's the land of gods. Maybe the pronounced "inside" sense is just what you wanted.
[edit] I missed that the vojjor there wasn't in the genitive. Is that an error or are you trying to use a word compound expression, something like "god lands"? Perhaps the vojes assikhqoyisir was an attempt to a similar expression, "prophecy man"? If so, I don't think word compounds work like this. I'd rather leave the first one in nominative and inflect the second one, but it's very iffy either way. Dothraki use a lot of compound words, so looser word compounds aren't that common.
Haha, oh god... I've missed the genitive marker for the third time, then. I was going for "vojjori". So "Kisha esh rhaeshaan vojjori" would be the correct form?