Hand of Fate 2

If you have The Servant and the Beast DLC, make sure you have the Shrapnel Bomb card as the ONLY artefact in your deck and begin The Chariot challenge. Here you will face armoured Blight enemies from time to time. You only need to destroy the armour of 12 enemies to unlock the shadow shard in Shrapnel Bomb. The key here is that the artefact has 6 charges, which is double that of many others in the game.

Use all 6 charges, making sure you are destroying the Blights' armour as you do, then from the campfire menu recharge your artefact. You gain 12% on your tracker every time you do this. Make sure to put Cave of Wonders in your deck, as it will always pull Shrapnel Bomb provided it's the ONLY artefact in your deck. Goblin Trader, Exploding Doodads and General Store are all helpful options as well. If you're impatient, throw a Soul Gem in your starting supplies, just make sure you also start with extra food for this challenge...

Rinse and repeat this process several times, and you can get the shadow shard and unlock this achievement in one fell swoop. Happy Hunting!