It was a Essence-- or Eimi that existed a long time ago. Before even the original seven seals even made themselves into what we know today. It was consumed entirely by The Golden Runesmith after he overthrew the last throne of Magi. He's been a problem for the Dreamlands for a very long time... Longer than you even could understand. — Troubadour; to the GoG Party
Magi is the former essence of pure arcana, magic, or otherwise known as 'Energy Manipulation'. It was part of a caste of pools that have since gone extinct called the 'Elder Essences'. The last remaining records of the Magi pool spread back even to far before the current reality that exists within the Philospher Stone was created. It was said that the Magi essence is still channeled through the modern day 'Arcano' and 'Mana' essences; potentially as its direct descendants.
Back when the Dreamlands was what there only was, and the mortal worlds intermingled within it in a place generally referred to as the 'Forgotten Realms'; the throne of Magi was Mystryl, or sometimes referred to as Mystra. The story that the Golden Runesmith sometimes likes to boast is when he killed such individual and claimed the powers of magic or 'Magi' for himself.
Magi was said to be 'energy manipulation' in its pure and most simple form, and was wielded by that of a C'tan who was well respected within the ancient history of the Dreamlands. After their assassination by the spellcaster Karsus, he usurped the throne, and the pool completely fused itself into him. The Magi essence is one of the main reason why The Golden Runesmith is considered too dangerous, wielding the powers of an entire elemental pool, alongside the energy he stole and consumed off of Mystra.
Magi has manipulation over other peoples magic, dispelling, altering, spell writing, and other such things. Individuals born with small influences from the Magi pool can go on to write spells and make magic items without the use of soul power. However it is a very demanding element requiring just as much energy back into it self that it puts out, or it risks destroying its host.
Magi Essence Crystals do not exist because of its exinction in pre-modern history.
