I am not that far into the story yet, and since I am taking it slow it can be a long while before I reach this part, but I am planning on throwing Asterios to 1v1 the eldritch child and see how it goes, will probably experiment with the lite version of Abby earlier on before deciding if I am going to take on this task.
Abby’s attack hits at 4-6 times, giving Asterios 20-30% gauge per attack, Asterios should have no problem NPing every one to two turns which coupled with an MLB Iron-Willed Training and his own defence buff enables him to take almost no damage. Abby’s NP strips buffs before damage, but as long as there is one previous stack of attack debuff, MLB Iron-Willed and a new NP debuff on that turn even her NP will be no threat.
An ungrailed Asterios solo likely won’t work for the big version since he simply lacks HP pool (and the attack), thanks to divinity even if Abby got attack debuffed by 100% Asterios is still going to take flat 175 damage every attack. Default MC gives 3000 heals every 7 turns while Asterios will take 3675 minimum damage assuming Abby attacks 3 times every turn. So he will lose roughly 675 HP every 7 turns in an ideal situation where Loss of Sanity/Witch Trial don’t mess up the rhythm too badly, all the while he will be hitting blue damage against a boss with HP numbering into million, sounds like a real challenge.
Loss of Sanity and Witch Trial is gonna be a big pain in the ass for this solo so I am expecting a lot of savescumming as well if I do it.
If anyone has a grailed (if max-grailed even better) Asterios with MLB Iron-Willed Training (shirtless Kirei), please let me be your friend.