Looks like Amazon pricematched Steams current price for Darksiders II, which is $24.99 (50% off). Use their 25% off digital games promotional claim code and the price drops to $18.74.
The game uses Steamworks, so Steam activation is required.
The promo code is OCTOFUN1, but apparently it’s one-use per account. I guess since it’s a Steamworks title, you could always make a new account. Use the code and buy the game. Activate on Steam and you would never have to touch that account again.