Embri is single accusative form of embar. Rōva is a class I adjective and takes the form of rōvor in the nominative and accusative for aquatic nouns. See more here https://wiki.dothraki.org/High_Valyrian_Adjectives#Class_I
Good question! It basically depends on their gender class, as well as the case and if it's plural or not. So an adjective like "Big" could have 8 different endings - 4 depending on the class, 2 depending if it's plural or singular, and 2 if it's nominative or accusative - and that's if I counted it correctly.
The infinitive form of the verb is: izūgagon
v. Obl. appl. [High Valyrian Verbal Prefixes: Oblique Applicative] C-fin. [High Valyrian Verb Tables: Consonant-final] to fear
Ñuhī zaldrīzī izūgilā. — You will fear my dragons.
From Dothraki Wiki: https://wiki.dothraki.org/High_Valyrian_Vocabulary