Start a campaign with seed 49004:


At the start you will get the following choice:


Pick the relic, but skip it for souls:


Follow the path on the left to the shop:


After the first battle, skip the card again and choose souls:


You will now have enough souls to buy double cast in the shop:


Continue the path on the left:


Upgrade double cast to triple cast:


Be aware that it has turned into a destroy card, which means it will be destroyed from your deck after being used so make sure to only use it on a utility card with a perk. To obtain one of these cards, just simply keep following the left path and at some point you will reach this question mark:


This gives you the following option:


Choose to fight instead of paying souls. After the fight, you will get the overloaded agility card, which is a utility card with a perk you need for the achievement:


Now just simply use triple cast followed by overloaded agility and the achievement is yours.