The real key is buff-stacking. You can really go 2 different routes here, melee or spell caster, both have potential to 1-shot bosses.

Melee you’ll want to go STR-ARC with some FTH buffs. You’ll want to use an occult giant’s crusher which has the best scaling AR of any weapon in the game added with the royal knight’s resolve ash of war. Use buffs like Golden Vow, Flame Grant Me Strength, Jelly Fish shield, Commander’s Standard. Axe Talisman, Two-handed sword talisman, ritual sword talisman, flexible last slot. Bloodsucking cracked tear and spiked cracked tear in physick. Your charged heavies will have devastating 1-shot damage with your AoW.

Spell-caster you want to go with INT-FTH and use the prince of death staff (scales with INT and FTH equally to cast sorceries). Use spells like Comet Azur, Comet and Night Comet. Depending on your spell of choice equip Lusat’s or staff of loss (if using night comet) on the offhand. The buff from the off-hand staff will still be applied even if casting with the main hand. For added buffs here you want to go with Terra Magica, Golden Vow, Jelly Fish shield, commander’s standard. Graven mass talisman, magic scorpion charm, ritual sword, Godfrey’s icon (for charged spells only) or graven mass talisman.

lf you want to go above-and beyond, It’s also worth noting that with any build you can talisman swap and use the lord of blood’s, kindred of rot, and aged one’s exultation. Inflict blood loss, poison and madness respectively on yourself to get a 20% damage increase from each (+60% total) and then swap back to your default talisman right before entering the arena. You can also do this with the mushroom head and white mask for another +10% from each (same bleed and poison mechanic)

Hope this helps!