I think that they are a powerful force and we should be careful around them. In a quest, we saw that the Abyss Heralds and Abyss Lectors are able to use human language and converse with the Traveler. The Pyro Lector that posed as Enjou in a quest in Enkanomiya was able to get a human body and was able to talk to the Traveler without any limit on his conversation skills. In the conversation, he mentions reptilian people, also known as the "Vishap-people," who have vertical pupils and how he betrayed them. Though he's pure evil in a sense, we get to know that he knows a lot about the history and considers him a marginal person in the Order than others who are willing to do anything for the princess. I think that we haven't seen any extremely powerful opponents from the abyss yet. Opponents like Dvalin or Andrius were worthy of being called boss enemies because they had a vast size and aggressive nature to them. Judging on that, I'm sure there must be Abyssal Dragons or beasts that we will encounter someday, and it will be tough to fight them. If Celestia had to attack Khaneri'ah, it could only mean one thing: Khaneri'ah was a very powerful nation. Their Art of Khemia reached a point where they could create life out of nothing, which is indeed the epitome of an ability.