This page covers the entirety of the Epic Battle Fantasy 5 final boss fight. This page will contain sizable spoilers.
Much like their predecessor Akron and unlike Godcat, the Devourer does not interact directly with the party at any given point (in fact, the existence of the Devourer is hardly implied until the actual final battle). They are fought at the very end of The Beyond, in a two wave fight.
It is highly recommended that the player eat all of the Steroids and do the bonus dungeons before taking on the final battle.
Wave 1: Cosmic Gigalith
The Gigalith is capable of altering its elemental weakness at various points in the fight. It also buffs its Evade by 15% or 25% on Hard/Epic when doing so, making its already solid evade become immense. As such, the player should come with an evade-lowering summon, such as the Putrid Worm or NoLegs Doll summons. Try to have your main attackers equipped with the appropriate extra skills to have as much elemental coverage as possible; while non-elemental attacks will always work, they'll deal significantly less damage due to the Gigalith having -300% resistance to its chosen weakness.
The Gigalith mainly uses multi-target physical attacks from the Ice, Wind, Bio, Thunder and Fire elements, with the occasional multi-target Enchantment or Syphon. Try to have resistance to those 5 elements, it's also a good idea to bring the Cutie Worm summon along, since this'll allow you to remove the Enchanted status the Gigalith inflicts on your players.
The Cosmic Gigalith will counter attacks with its own, usually aimed at the character who attacked it. Auto-skills will also trigger counters unless it's a summon (before the v2 update summons also triggered counters). If a player has the Target status (inflicted by the Target Badge or Agnry Faic flairs when defending or by throwing a Brick), then all counterattacks will be redirected to that player, regardless of who attacked last (as such, an Invisible tank can help negate all of its counterattacks); if the character that attacked was inflicted by Lovable, the Gigalith will redirect its counter to a different unit most of the time (this particular interaction seems somewhat broken, the Gigalith will very occasionally counter a Lovable player anyway). It's worth noting that player counters are disabled during the Gigalith fight, to prevent a player and the Gigalith from ending up in a countering loop.
Once the Gigalith's health gets lower it'll start using its Scorching Lasers, dealing high non-elemental magic damage to all allies and Scorching them, the lower the Gigalith's health is, the more often it'll use its Lasers, until eventually the Gigalith only uses Scorching Lasers.
On Hard or Epic difficulties the Cosmic Gigalith will use Doomsday on death, dealing extreme Dark damage and leaving the party vulnerable to being wiped out by the Devourer, which is capable of attacking immediately afterwards.
On the turn you're ready to kill the Gigalith, use the Viking Monolith summon if you have enough SP, since killing the Gigalith (particularly with the Small Cloud flair) is going to pretty much fully refund your SP, and the extra turns give you some leeway for the Devourer. If playing on Hard or Epic, also make sure to take protective measures against Doomsday before landing the killing blow, such as Enchanted from the Angel Mirror summon, Morale from Death Metal or Stumpy Gloop, or Auto-Revive from Nine Lives.
There's a bug that causes Doomsday to scale with player Summon Attack instead of the Gigalith's Magic Attack if it gets killed by a Summon, which will cause it to deal negligible damage, this can be potentially abused to make Doomsday a non-issue outside of its Scorch.
Finally, it's worth noting that defeating the Gigalith, fleeing the battle, and then saving will permanently halve the Gigalith's maximum HP, making any further attempts at it significantly easier. Additional defeats on the same save file will not halve HP further. On harder difficulties, the player may wish to rush the Gigalith with Limit Breaks immediately, then flee when the Devourer shows up. This way, when the player "properly" fights the Gigalith, they only need to clear out half of its health, making the final boss fight easier. On the other hand, some players may wish to not kill the Gigalith until they are ready to fight the Devourer to retain the higher difficulty as a result of having to fight the Gigalith at full health.
Once the Gigalith is dead, take a brief breath. If you are playing on Hard or Epic, you have the Doosmday to contend with, but otherwise the first chunk of the battle is done. And keep watching that screen because...
Wave 2: Devourer
- "ALLOW ME TO INTRODUCE MYSELF. I AM YOUR END!"
- ―The Devourer, Epic Battle Fantasy 5
Unlike Godcat the Devourer will burst right in, meaning that if you've struck the Gigalith down with your last turn, the Devourer will get right to obliterating your party. Until the Devourer gets to 29% health (and uses Delete Earth), the party can still run from the fight. If you barely made it through the Gigalith (or got slaughtered because the Devourer caught you unawares), it is a good idea to Scan the enemies, flee, and return under more favorable conditions.
The Devourer possesses a slew of vicious attacks, including Bomb, Fire, Earth, Thunder and Wind elemental attacks. Keep in mind that some of their multi hit attacks do varying damage on each hit. While his attacks are 50% elemental at best, resistance to his most used elements (Fire, Bomb and Wind) definitely still helps.
The Devourer has thankfully simple resistances, absorbing Bio and being weak to both Holy and Dark. Plan accordingly; all of the party members have an attack of the relevant type in their main skillset (NoLegs and Natalie having both), so consider sticking to those elements for your main attackers.
Each appendage has a different role: Slimy Tentacles are magical attackers that focus on inflicting status effects, Spikey Tentacles are powerful physical attackers, and the Evil Eyes are supporters that can buff and cleanse statuses from the enemies or reverse the buffs on your players.
The appendages all absorb Bio, but while the Evil Eyes are weak to Holy and Dark just like the Devourer, the Tentacles are vulnerable to Fire, Ice and Lightning instead. The Eyeballs also resist Water, though this probably won't be too relevant through the fight.
Other than the appropriate elemental resistances, it's also a good idea to have at least a few characters that are resistant to Confuse and maybe Freeze, since otherwise the Devourer's Sonic Wind and the Slimy Tentacle's Dev Ice can incapacitate your entire party.
The first priority is to take down the Devourer's appendages (and then make sure to keep them down), having Anna with triple status gear (Alchemist's Bow, Blue Elephant and Red Dress) instantly kill all of them with Annihilate can be a good choice (just make sure to buff her Accuracy first); though strong offensive limit breaks can also kill them as long as you inflict a maxed defensive debuff first. Afterwards, try to make it a priority to kill any appendages that respawn, Spikey Tentacles and Evil Eyes in particular should be taken care of before they can get a turn, if you can't manage to kill them in one turn then use statuses to incapacitate them (you'll need Anna with double status gear to reliably Stun the tentacles). The Slimy Tentacles are the least dangerous, while you should still try to kill them as fast as possible, as long as your party has Bless on to prevent their status effects, their damage alone is not too threatening. Both tentacle types can be cut if they receive enough damage at once, which makes them only able to use Spray Acid to inflict Poison (below Hard) or Virus (Hard and Epic), the Virus in particular can be threatening if any of your characters gets inflicted, since it can spread to the Devourer and its appendages and they'll heal from it (if Virus goes out of control, remember you can always use Purify on foes to remove it ). As a sidenote, keep in mind that if 2 or more of the Devourer's appendages are inflicted with Freeze, Stun or Syphon, the Devourer will use Dev Heal without taking up its turn to remove those, so you can only lock down one appendage at a time with statuses.
As for the Devourer himself, try to keep Curse and Weaken on him at all times, not only will this help by keeping his stats debuffed, the statuses will also boost any Holy or Dark-elemental attacks you use on him.
Once the Devourer reaches the 74% and 49% HP thresholds, he'll use Charging Sphere to Dispel your party while giving himself the Charge status, while on Normal and below this is followed immediately next turn with Giga Doomsday, on harder difficulties he may wait up to two turns after Charging before using it. First of all make sure the party has Bless when you approach the thresholds to prevent getting Dispelled, and afterwards use the Stumpy Gloop summon to inflict Morale on your entire party to protect them from Giga Doomsday, then just make sure to keep your health high while cleaning up any appendages (this'll prevent them from either breaking your Morale threshold or killing you after you're left with 1 HP).The one good thing about Giga Doomsday is that it inflicts so much damage that your frontline is gonna instantly get their Limit Breaks back, which is helpful given that the Devourer will generally summon all his appendages back after each Giga Doomsday.
Finally, going down to 29% HP will have the Devourer use Delete Earth, preventing the party from fleeing and inflicting the Delete status that makes the party slowly accumulate damage, with the amount of damage rising with each turn. Thankfully, the damage scaling starts slow, so you should have more than enough turns to finish the fight off; if you're in a bad situation when the phase starts, consider using your Chili Peppers to replenish your Limit Breaks again, since this is quite literally the last fight, there's not much of a reason to save them anymore. As a final reminder, killing the Devourer will immediately end the fight, regardless of any remaining appendages.