In Orson Scott Card's Speaker for the Dead, he proposes a scale of alienness: first, there's the utlanning, a member of your tribe; second, the framling, a member of your species but of a second tribe; third, the ramen, a member of a seperate, sentient species that you can reason with and live alongside; and fourth, thevarelse, a member of a sentient species with which there is no reasoning. These days, Card is completely batshit insane, but back in the day he had some good ideas.
In Chrono, there are a number of ramen; the mystics, the reptites, the demi-humans. (Note that just because you CAN live peacfully alongside a species doesn't mean you WILL.) Lavos, however, I beleive is varelse. It has showed sentience, (although NOT in its ability to corrupt people; people, eg Queen Zeal, corrupt themselves in pusuit of its power) but never communicate with people--in CC, it's the time devourer that communicates, and it's half-human, remember. Lavos can't be classified on our scale of morality, and it can't be reasoned with, not because it's stupid or stubborn, but because its thought run (metaphorically) perpindicular to human thought.
Again, that's not to say it's vastly smarter than humans--though it is more powerful than any single human--just that it exists on another plane of sentience. Its simple varelse.