Lunar Ramuh

Lunar Ramuh is an optional boss in the Game Boy Advance port of Final Fantasy IV. It is fought during Cid's Lunar Trial at the Lunar Ruins. When beaten, the player obtains the Fiery Hammer which is Cid's ultimate weapon, and the Grimoire LR which if used as an item, summons Lunar Ramuh to deal 9999 thunder-based damage to all enemies. Using up the Grimoire unlocks the trial door again.

Strategy
As one would expect, Lunar Ramuh uses primarily thunder attacks like Thundaga, Blitz and Lightning. However, none of them are truly dangerous, although their damage output is high it's not fatal. As long as Rosa or Porom are in the party to heal, the battle should be simple to win.