@Grahamhsu
Bear in mind that in order to have 1.5K HP, you'll need to be at 50 Vitality, and that to use Regalia you'll need to have at least 20 Strength, 14 Dexterity and 12 Magic&Faith.
Even if you start out as a Knight (It has the most balanced start up for those stats), you'll still need 53 Soul Levels to get all those stats (and that's counting out any balances and corrections that you might make in order to compensate any other low level stats), so you'll need to be at least SL 67 to use Northern Regalia effectively.
Also, to get the entire boost needed for the 540 attack power, you'll need to be in either Pure Black or Pure White Character Tendency, otherwise the attack power of the Regalia will drop massively, to 270
But that's not the hard part, you'll also need to complete the Flamelurker fight at NG+, which at those low stats will be a pain indeed, because you won't have access to the "good" weapons needed, nor will you enough magic points nor intelligence points to use the spells needed for a Stealth approach (Poison Cloud or Death Cloud). You could try using a Heavy Crossbow, but you'll need to proficient in lock on skills without the Flamelurker actually seeing you.
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