Eternal Card Game

I've found this one quiet easy and fast to unlock by launching a gauntlet :

- Create a Fire deck and make sure you have 4 of the Corrosive Dagger weapon (cheap to craft) ;
- Put a bunch of 1 cost to 3 cost unities ;
- As well as a lot of weapons (very important) ;
- And some Torch, or anything that can swipe the enemy board.
(You can complete with the Chemical Rounds spell if you like - wich causes 2 decay damages).

I put a basic 2/1 Ronin at first and I upgraded him with all the weapons I had, included the Corrosive Dagger wich gave me Decay. I got rid of the enemy units with spells or other units. I kept two on the board so they can defend my Ronin. In a few rounds, my Ronin was 12/14 or something like that. From this point, attack twice (or more) with this unit, win the game (or not, whatever) and the chivo should pop up.
Took me about 5minutes.

If you can’t be bothered to craft a specific deck or any cards for this achievement then there is great campaign mission for you to get this achievement easily.

Head into the Awakening campaign, then chapter 3, mission 1 called The Scrapyard. The mission rules are that all units have decay so you can play any deck you like as long as it has a good number of units as you’ll frequently be trading stuff off to the point of death.

With the amount of cheap grenadins the opponent throws at you it is probably easily possible to do this achievement in one game if you delay killing them. If you don’t get it in one game then simply run the mission again and it will likely pop after a 2nd or 3rd game.