Carian Retaliation is one of the most useful shield-based Ashes of War in Elden Ring, turning parried incoming spells into retaliating Glintstone daggers that deal very good damage. The damage of the daggers scales with the upgrade level of the shield and the power of the reflected spell, ie the stronger the magic, the higher the counter damage. It also parries weapons well on its own.
To find Carian Retaliation, progress through Ranni’s quest line until she is accepted into her service, then head east of her and Selivus’ Rise.
Drop onto the stone roof, then onto a lower platform, and then down the ladder that leads into the building itself. There, speak twice to Pidia, the Carian Merchant, to put his inventory up for sale.
Carian Retaliation is one of his items that sells for 3,000 runes. He also has some other useful items: a Larva’s Tear for respecing stats, Heavenly Dew for absolution, and a Ritual Pot for throwing items.
Finally, head to either Master Hewg or a Place of Mercy and apply Carian Retaliation to any shield that can take it and begin parrying any spell or incantation that dares approach its power. Keep in mind that it also acts as a standard parry. So when placed on a buckler or other shield with a tall parrying frame, it does double duty as a spell and weapon defense.
https://www.gamepur.com/guides/where-to-find-the-carian-retaliation-ash-of-war-in-elden-ring Where to find the Carian Retaliation Ash of War in Elden Ring