|1~99||Up to 750,000||Earth, Beast|
Sounds easy were it not for Firstborn's Innate 85% Evade ability that--as its name suggests--allows it to evade all attacks with a 85% chance. There are at least two ways to handle this sneaky teddy. First, you can use the Guardian's Soul Mirror to reflect its own attacks.
85% Evade doesn't trigger for reflected attacks and Firstborn's attacks all hit like a truck--even to itself. What you can do is field a Guardian or two and routinely put up Soul Mirror for all your party members. Make sure to equip Prescience to always go first.
To speed up the battle, you can purposely boost Firstborn's physical attack. Just watch out that Baby Bubbles dispels Soul Mirror, but unless you're extremely unlucky you should have enough BP to put it up again. Another thing you can do is make some party members ghosts.
Two, if you're persistent and keep unleashing attacks on Firstborn, you'll eventually hit it. To improve your odds, you can use Dual Wield, Triple Wield or Quad Wield for multiple conventional attacks or Echo and Chainspell to cast multiple spells.
The first time Firstborn gets hit, it'll become angry. While angered, it occasionally uses Feed Me to boost its BP by 3. Keep going and the second time it gets hit, it'll topple over. When this occurs, 85% Evade will be disabled, allowing you to attack normally.
Should Firstborn survive your onslaught, it will use Nap Time's Over on the next turn to stand up again. To maximise your profit, your characters should be faster than Firsborn to attack before it wakes up. After the big baby stands up, just repeat the process to knock it over and eventually knock it out.
For a chance of a one-turn KO, you could rely on the Ghost Mage Onslaught (discussed in our Recommended Builds section). However because you need to hit Firstborn two times with 15% accuracy, there's a chance you won't do enough damage to KO it in one go.
If that happens, you can reload and try again (and again, etc). Or if that's too unreliable for your liking, you can begin your onslaught after building up maximum BP instead, so even if you don't KO Firstborn in one turn, at least you won't be a sitting duck afterwards!
Note : We recommend not saving after defeating Firstborn. Instead, keep it alive so you can steal rare Unearthly Buns from it using the Thief's Prince of Thieves. After each successful steal, run from Firstborn so you can repeat the process until all of your characters' stats are maxed out.