At the highest difficulty the Iron Giant has 80,000,000 HP. It sports a ridiculously high ATK of 2,400 which can easily destroy the player without proper preparation.
The Iron Giant's skill arsenal, however is rather limited as it can only use these attacks: Meteor (magic damage (10.67x) to all units), Reaper (physical damage (7x) to all units), The Pressure is tightening! (fixed damage (1000), inflict paralysis and fixed damage (0.01x) as MP drain (100%) to all units), The pressure is overwhelming! (Fixed damage (1000), inflict paralysis and fixed damage (0.01x) as MP drain (100%) to all units) and Power is being released! (increase ATK/DEF/MAG/SPR (100%) for 3 turns to self).
Although it can attack up to 7 times per turn it is programmed to attack only 5 times per turn for most of his turns. The Iron Giant will use Meteor and 4 normal attacks, every turn while above 50% of HP. The Meteor cannot be sealed by Sealing Blade or Manufacted Nethicite.
It has several thresholds which are a bit more tricky. At 80%/60% HP it will use Reaper, Meteor and 3 normal attacks and end its turn. At 50% HP it will use The Pressure is tightening! and follow with its regular attack pattern. At 40%/20% HP it will use Reaper, Meteor, Power is being released! and end its turn, but on the following turn it will follow with The Pressure is overwhelming! and two Reapers and end its turn.
Below 50% HP its pattern changes slightly, now casting The pressure is overwhelming! and Meteor once every turn, while having a 34% chance of casting a second Meteor. However, once three of the guaranteed Meteors have been cast, it will use all its 7 actions per turn, by casting Power is being released! on the same turn and following with either two normal attacks or one Meteor and a normal attack. After doing any of these, it will add Reaper on its attack rotation the next turn.
The Iron Giant has no innate elemental resistances or weaknesses, is immune to all status ailments and vulnerable to all stat breaks.
The Iron Giant is a powerful, but simple enemy. Its attack patterns are fairly predictable and can be easily managed, however, the player will need some preparation to withstand its strong attacks. Even with stat breaks as high as 50%, the Iron Giant's massive ATK stat will guarantee high damage if any of its physical attacks are successful.
A Tank with full physical evasion will deal with this problem, but if this is not possible, the player will need to prepare a rather bulky Physical Tank (one who can also Cover attacks) with at least 10,000 HP, as high as possible DEF, strong defensive buffs and damage mitigation.
Assuming the Tank can survive the normal attacks and Meteor, the player will need Reraise, as the Iron Giant's Reaper ability will easily destroy the Tank in a single swing if it cannot avoid it fully. As such a Healer which can Dualcast both a Reraise ability and a heal ability is recommended, otherwise the player will have to distribute these tasks between two units.
For damage it is highly recommended the player uses magic damage, as the Iron Giant sports a potent 300 DEF but a pitiful 35 SPR, ensuring 12 times more damage from magic damage sources. Any seasoned Mage is useful for this, be it nukers like Dragonlord, Blossom Sage Sakura or Emperor, or chainers like Barbariccia, Pure Summoner Rydia or Lexa. One very useful unit is Lila as many of her abilities have the unique property of being physical-type and deal magic damage. This means that Lila can profit from physical killers like Man Eater yet still inflict magic damage, making her by far the best damaging option possible for this battle. If a Light Imperil is added (provided the player has earned the Holy Wand from the Chamber of Arms), then the damage will skyrocket, even more so if the player has unlocked Open Eyes - Flash to triple cast her abilities.
It is however, advised that the player is careful, as inflicting too much damage at once may trigger thresholds when not all buffs have been prepared or, risk crossing more than one threshold at once (which will warrant just as many retaliations). Due to the trickery that the second half of the battle may present, it is usually recommended for the player to cross one threshold at a time and reach as close to 50% as possible, then destroy the Iron Giant all the way down from there instantly.