The Monado Mandala is the final dungeon of Persona 2: Eternal Punishment.
The Monad Mandala seems to be referring to the ideas of the philosopher Gottfried Wilhelm Leibniz, who postulated that the "monad" was the smallest individual unit of spiritual substances, the spiritual "equivalent" to the atom. In Gnosticism it is the spiritual source of all things that flow with pleroma and is the true God from which all aeons originate.
"Mandala" is a generic term for any plan, chart or geometric pattern that represents the cosmos metaphysically or symbolically, a microcosm of the Universe from the human perspective.
- Persona 2: Eternal Punishment: Final dungeon