I found this best to do in CO-OP and below is a quick guide on how we set-up our units and what two decks we used to knock this out. Our strategy actually helped us get to wave 50. Having a deck set-up that's a little more offensive (Forge) helps to beat the early waves, and then having a deck designed with a lot of siege units and guard units (Atriox) for the later game really worked. I will say the Hero's, especially Atriox are key, due in large part to their large amount of health and shields, as well as range and damage. Check out the guide below from my channel and the written description! Not a bad achievement if you can get it all set-up.
Decks we used:
Starting Army: Full Metal
Starting Army: Bulletproof
For those that can't watch the video, our set-up is pretty simple. Initial waves (1-10) just hold points B and C while your building up your army. The player using Forge should be the one mainly defending B and gathering energy, while the Atriox player holds energy and calls in Reavers, Blisterbacks and Atriox Chosen. Make sure to push units up far enough to the choke point between points B and C on the enemy spawn side so that they are not moving along the ridge. This ridge is where you want to start setting in as many Blisterbacks (with the Enduring closer to the front in case they get destroyed as you will get the infantry units out of them) and Kodiaks. Use Atriox as well as your Ironclad Hunters and Wraiths to build a wall of troops at the choke point and not allow them to move onto the ridge. From there, the Forge player is protecting B, while you protect C from the front and build Reavers on C to fight the air waves. The remaining units, if set-up right, should not even get anywhere close to C. You should have this pretty well set by about wave 15, and from there you can use more leader powers and continue to build your forces. Don't worry about point A, as after each set of 10 waves the map is cleared, so the forces the enemy AI pushes there will be removed and don't need to be killed unless your grabbing energy. Gathering every energy is absolutely vital, so make sure both players are making a consistent effort to help with that whenever they can. This can also be done with three players, and that helps as it gives more troops and more people to focus on building the defenses. You know you will be set when waves don't even make it to your choke point as they are just smashed by all the siege units. Hope this helps!