Any way to farm Legendary Ink in Iron's Spells n' Spellbooks?

Right now I've been researching ways to farm Legendary Ink in Iron's Spells n' Spellbooks, but none of them seem good for where I'm at right now. I've heard getting Legendary Scrolls and putting them in the Alchemist's Cauldron has a 50% chance to give Legendary Ink, the only problem being that I don't have any Legendary Scrolls. I also heard fighting the Undead King gives Legendary Ink, but I'm pretty nervous. Haven't been able to find a video of the boss fight, or of the Catacombs in general. Plus, I'm in Hardcore and have a lot of stuff.

Right now I have full Protection IV Unbreaking III Mending Diamond Armor with Feather Falling IV and Depth Strider III on my boots, and Aqua Affinity and Respiration III on my helmet. Pretty much max gear except not Netherite and no Thorns, (I don't really like it) Soulspeed, and Swift Sneak. I have a Sharpness V Fire Aspect II Looting III Unbreaking III Mending Diamond Sword. I've heard Smite is better, because the Undead King is, well, undead. I'm currently trying to get that. I also am missing Sweeping Edge. As for food and healing, I have lots of Steak, as well as 6 Golden Apples and 2 Enchanted Golden Apples. I'm still rocking a Flimsy Journal with Greater Heal Level 1, Burning Dash Level 3, Summon Swords Level 3, Acid Spit Level 4, and Earthquake Level 6. Currently, using Greater Heal and Earthquake uses all my mana, and I can't even cast Summon Swords. I need to increase my max mana and mana regeneration, I just don't know how.

Now that you know my gear, should I fight the Undead King? Or are there better ways to get Legendary Ink?