I did it. After 16 runs, Yagluth was mine in hardcore mode.
I meleed Yagluth down with little difficulty. I used Frostner, shield, upgraded padded, fire resistance mead, medium health mead, tasty mead, fish wraps, lox meat pie, and blood pudding. Stamina and health were ample and not an issue. I would circle around it until the blue melee attack, then go in and land 6-8 blows with Frostner. I would then retreat and kite meteors. I found that the breath weapon can be easily avoided by sprinting towards him off to the side of it, as you can spin around him faster the closer you are. I had a single Fuling add during the fight, and I was glad I had my shield as I time blocked it and one shot it with no issue.
I have posted shots of this run up to my 20 shot limit. I had some more of my plains farm, my mountain mining operation that I will post if anyone is interested and link it here. I put captions on the screenshots to let you know what they were. There are shots of my seed, and my skills after the kill that I achieved without dying through a boss kill.
My hardcore rules are this- if you die, delete the character, start a new seed, the seed is random, no seed viewers, fully upgrade an armor set per biome before advancing, only natural skill advancement on weapons (no training dummies), use mods that reduce tedium but do not reduce difficulty of the challenge. I am no pro…I am a regular Dad that decided to go on this challenge after my son moved on to prove to myself that I could beat this game without being carried. I have posted on my runs not to establish myself as any kind of authority, but to share with the community what I learned, and in turn learn from the community in feedback. Thank you all so much for your helpful advice.
Now I need to decide what to do next. I beat it in softcore. I used elevated difficulty with mods. I beat it in hardcore. I suppose it comes down to giving creative mode a try, or perhaps moving on. If I move on, I will return as I do other games like Path of Exile which continue to pump out new content.
Edit- seems like adding text dumped the screenshots. [Photos here](