Dantalion is a rather quiet, private individual, it would seem. He constantly carries poise and an air of professionalism about him regardless of the circumstances he's under. His speaking style in tandem with this speaks of a higher social status and a great degree of wealth.

Boundless curiosity is a constant with him. He asks questions, listens to answers, and tries to decipher the unknown. Should something catch his interest, he doesn't stop until he's learnt as much as he can about it, though this can be somewhat slow-going. There's much to learn about the world, after all. In addition, he's rather studious, usually seen reading or carefully observing the world around him. He will trade information for information, striking deals to get what he desires — would you like to learn about magic? Well, why don't you trade him for information about something of equal value? Money and material wealth do not interest him; everything comes back to science.

He's a rather skilled mage, able to expertly perform what he calls "moon magic", a form of magic which he explains encompasses both light and dark. He strikes others as patient in how he carefully explains this to any who don't understand, and repeating questions do not seem to bother him. He's even willing to demonstrate his prowess, being cautious not to hurt you in doing so — and should you find yourself hurt, you'll have a healing spell cast on you immediately. He's so very kind and calm, exactly like how one would think the moon ought to be.

But

...Why does he smile like that?

Dantalion is not who he says he is; he'll tell you that his name is "Ebalon" and smile sweetly, politely, but all of his interactions with others are rather measured and controlled. With semi-rare exceptions, he never allows his actual identity to slip through. He's impersonating someone, you see, a young man he killed named Harque Ebalon. Should you find out that his true name is Dantalion, you either know too much and must be eliminated immediately, or you've been trusted with sacred information. Unfortunately, the former is far more likely than the latter.

He is a deceptive and manipulative man under the surface; all niceties are merely an act, since he's supposed to be "Harque". Dantalion will act as though he cares, look out for others, and generally play the part of the meek and quiet Harque. Behind this, however, he is cold, calculating, and constantly observing others to see what use they can provide to him. Those without any "use" are rather swiftly discarded or of little to no interest — however, those with some sort of perceived use to him, be it minor or major, will find themselves targetted and treated with a certain kindness. Up until they wear out their usefulness, however, at which point Dantalion is very quick to "take out the trash".

His plans for destruction, devestation, or otherwise usually take a very long time to stew, and he's quite meticulous in how they're performed. Every little detail must be perfect before and during execution. People have to be coerced and swayed to his side, trust must be built, and he needs sufficient time to worm his way into the hearts and minds of others to ensure everything goes according to plan. As a result, his plans can take ten or more years to be put into place, but this isn't of consequence to an immortal man.

As a high-ranking member of Henir's Order — a doomsday cult, in simple terms — Dantalion utilizes your typical cult coercion tactics to sway people. He is very patient with this, and hardly expects things to happen within a day. It's all based in trust, and from trust it's based in loyalty. Of those who he commands, he expects absolute loyalty; going against him is not an option unless one wishes to meet an untimely demise. If that's the case, he's more than willing to handle said demise as painfully as possible.

When the more "real" side of him bleeds through his measured interactions, Dantalion is quick to anger and even quicker to destroy, often going for something catastrophic in damage. He has a real sadistic streak about him, including track records for human experimentation and an over-the-top love for discovering what can "break" the mind and body, as well as discovering the unknown or simply seeing "what would happen if X happened?" While curiosity is a driving force, this curiosity is not pure and innocent in its intent; there's always something to be found and something to be used to further his own ends.

Should he mess up at all and allow something to slip through the cracks, Dantalion is swift to undo it with mind magic, erasing the offending memory completely from the other person's mind so that he can continue to operate as he always does: in the shadows and behind the backs of those he might feasibly convince to trust him.

SHAPESHIFTING: His most glaring ability is that of shapeshifting into any form he would like. His preferred form at the time is that of Harque Ebalon. His real form is unknown as of current canon, though it's believed he's either a demon or an eldritch horror or an eldritch horror-demon in reality.

IMMORTALITY:As Dantalion is over 1000 years old, his immortality seems to be based entirely in lifespan like a vampire's would be. Canon implies that he is perfectly killable through other means.

MOON MAGIC:The power of the moon has two aspects, the light and the dark. The light is responsible for the areas of healing and protection though it can be used to inflict injuries; the dark is the more violent aspect that's mostly used to harm. The light aspect also has a freezing effect to it if needed, shown by other moon magic users in-game. Dantalion typically summons apparitions of the moon when casting large spells and has a crest that will appear at his back when he uses magic. The crest is white when utilizing the light aspect and purple when using the dark. Dantalion can create sigils on the ground (the sigil will show up white if light-aspected, dark purple if dark-aspected) that will explode with magic on contact as well. This link has a solid list of spells he utilizes in his boss encounter. This video I took of his boss fight pretty accurately showcases how he looks while fighting, though it may be somewhat incomprehensible to people unfamiliar with this game.

TELEPORTATION: He can teleport using moon magic like so, leaving an apparition of the moon behind when he does. This can be used under both crest colours and the colour of the moon will change accordingly (white for light; black for dark).

MIND MAGIC: Dantalion has access to mind spells including modification, falsification, and deletion of memories. He puts his target to sleep before doing this.

SLEEP MAGIC: Exactly what it says on the tin. Zzz...

SPELLBOOK & STAFF: His spellbook and staff are able to be summoned to his side at will. Dantalion will frequently flip through his spellbook mid-fight to cast spells and uses the staff as an arcane focus.