Magical Magus initially appears as a sub-boss in Persona 3, found on the 98th floor of Tartarus in a group of three. They impede the player's progress and must be fought in order to continue. They are later found in the Tziah Block of Tartarus, between floors 123 to 138 as regular enemies.
Personas such as Flauros and Sarasvati will be useful in dealing with the Magical Magus. Flauros can target their weakness with Maragi (Agilao in FES) and in the event one of them manages to use Makarakarn, Sarasvati can use Mabufu to remove with without the protagonist receiving damage and protecting him from any further Ice attacks during that turn. Taking Junpei Iori and Koromaru along and setting them to the Knockdown tactic will allow for more All-Out Attacks. Mitsuru Kirijo may also be taken along as a healer, since she will take reduced damage from their Ice attacks.
The Magical Magus returns in Persona 4 on the 6th and 7th floors of Yukiko's Castle. It drops Supple Metal when defeated. Selling 10 Supple Metal at Daidara will unlock the 5-Iron weapon for the protagonist. It also drops a Demon Statue, a quest item required to complete Quest 02: Acquire a Demon Statue.
Magical Magus appears on the sixth and seventh floors of Yukiko's Castle within the Midnight Channel. They will attack using their Agilao spell unless they stand by with a message that they are gathering magic power, after which they will use Maragi. They are weak against Light but if the party does not have access to the Hama skill, they can be incapacitated using Yosuke's Makajam or Chie's Skull Cracker skills.
After being defeated, they may drop the Supple Metal material. Selling 4 Supple Metal at Daidara Metalworks will unlock the 5-Iron weapon for the protagonist.