Mentar are a curious and mysterious species. Their name is Matoran for "ghost" or "phantom", and appear out of nowhere, doing what they were sent to do and fading back out into nothingness. All Mentar have the innate ability to extract souls for living beings. Someone who is killed by a Mentar will become one instead of going on to the afterlife. They are the bane of countless militaristic organizations.
Tahrar is the leader of the six Elite Mentar. He is a master of his element, having the ability to heat his body up to millions of degrees Celsius being able to travel at superspeed by literally turning into fire. He can also combine his gravity power with his skills over fire, creating micro-sized suns! A very level-headed tactician, the other Elite Mentar depend on him to lead them to victory at whatever Ma-Taru commands them to do. He is very much respected by his teammates, and he is able to speak a little but of Matoran.
Guuzar is the only female Elite Mentar, and is very wise and calm. She is a patron for unity in the Mentar community, and she is fluent in Matoran. She has multiple powers, including water-related skills, manipulating the pressure (any kind -- including air), and controlling the weather. Her concern for unity does not make her any less evil than the rest of the Mentar. She just has as more peaceful way of showing it.
A very cold-spirited Mentar, Kohzar is the most silent Mentar -- even through Mentar are silent beings to Matoran-speaking races by nature. He acts as a secondary commander of the Elite Mentar, only listening to their collective leader: Tahrar. Kohzar's ice skills are so powerful that he could even freeze the sun. He strikes a balance to Tahrar's fire power, but despite this, he looks up to the Fire Mentar. Kohzar's secondary skill is power over Sonics.
Leerar is the least intelligent, but not by any means stupid. He can be somewhat hyperactive, often acting before really planning out the events in advance. He is overconfident, naiive, and his plans and wants are never set in stone. He is scatterbrained. Leerar has powers over Air and Poison.
A particularly devious Elite Mentar, Nurar has powers over Earth, and possesses all psychic powers, from mental blasts to advanced molecular telekinesis. His crossbow's arrows are tainted with a venom that can temporarily paralyze or "confuse" a foe (a "confused" person will mistake his allies for his enemies -- a type of illusion with a specific purpose). He has no respect for non-Mentar races, but he is fluent in Matoran. Nurar is the only Mentar immune to psychic attacks. On top of the standard defenses of Mentar, this makes Nurar's range of weaknesses that much narrower. During a conflict, he will negotiate sometimes, but only when there is no other option. He is by far the most feared Mentar by outsiders.
Like Leerar, Panzar is also the jovial type. Having trouble staying serious even in times of danger. His protosteel energy Axe can shash through anything that is solid and not made of protosteel. He manipulate stone through his axe, and his Zamor launcher can use magnetism to disable his opponents. Panzar is incredibly bitter about being a Mentar, but he understands that this his is purpose now. He does not speak any Matoran, so when he talks, only the Mentar can understand him. Panzar is noted for being the most merciful of the Elite Mentar, mostly because he has been a Mentar for the shortest time.
The Onimentar are the backbone of Death Haven. People killed by a mentar (or who are sent to Death Haven by Karzahni) become Onimentar. However, only the "warriors" assume the form similar to the elite mentar. The Onimentar soldiers are almost always seen on Hagaia, horse-like rahi with amazing speed, swinging their scythes in there air as they charge their opponent in large groups. All mentar wear the cloaks over their heads to hide their identity. Even Ma-Taru would become mentally disturbed if he were to witness these death-like creatures' identities. One slice from an Onimentar's scythe will "scoop" the soul out of that person, killing them instantly. Their soul will then go to Death Haven where it will receive an Onimentar body.
Hagaia are the horse-like steeds of the Mentar. They receive whatever powers traits the rider has. When a Mentar is not riding a Hagaia, it is very vulnerable to attack.