Madeen is disguised as a moogle named Mog, who lived and grew up with Eiko Carol in Madain Sari. When Zorn and Thorn kidnap Eiko and take her to Mount Gulug, Mog comes out of Eiko's pocket and goes into Trance, revealing herself as the eidolon Madeen.
Madeen urges Eiko to use her special ability, Terra Homing, which eliminates Zorn and Thorn. Afterward, Madeen reminds Eiko she will always be with her before disappearing entirely. Madeen is never referred to as a male eidolon, even after abandoning its female form, so this is the only game in which it is assumed to be female.
Eiko can learn to summon Madeen for 120 AP from the Ribbon add-on, which is obtained as part of the story when Madeen is first revealed to Eiko. Madeen's summon attack is Terra Homing (テラホーミング, Tera Hōmingu?) that deals Holy-elemental damage. Madeen's spell power increases with Eiko's level (see here for damage formulae), and costs 54 MP to summon.
Location: Memoria, Treno (Eidolon Master in Card Stadium)
Summons Madeen to deal holy damage.
Madeen can be learned from the Cheer Staff by the Summoner class. It uses the most MP of all the summons, taking 36 MP and needing 300 AP to master. This summon deals Holy-elemental damage to all targeted enemies, and has a Magic Power of 52. It is stealable through the ability Steal: Ability, and is also susceptible to Return Magic and Absorb MP.
Maduin is a Holy-elemental esper, and similar to its Final Fantasy Tactics Advance appearance, deals Holy damage to all units within a large area, and is learned by the Summoner from using the Cheer Staff. It requires 350 AP to master and 24 MP to cast.
Madeen appears not as a summon, but a boss.
The description of Maduin's Fang refers to the Final Fantasy IX Madeen as Maduin, marking the first and only time he shares the same name with Maduin from Final Fantasy VI in the same Final Fantasy title.
Madeen is the sole eidolon that Eiko can summon. It performs Terra Homing when summoned.
Madeen appears in Eiko's Ultra Soul Break Guardian Mog and is also a 5★ Summoning ability.
Madeen appears as a Shine-elemental card.