Kingdom Rush ReVengeance - Ruins of Castle Blackburn Iron (Impossible)

This is by far the hardest level I've completed. As you can tell, you only have 3 towers: DKs which aren't terribly well suited at stalling large hordes, swamp things with poor crowd control and mausoleum which isn't amazing at killing Bone Crushers. However, every once in a while your towers get Blackburn's damage buff, which makes them incredibly strong for a few seconds. Despite this it was really hard to find a good balance between towers and utilize the buff fully. I probably spent 8-10 hours on this before refining my strategy. What I did was completely abandon swamp things and focus on upgrading mausoleums while also building as many DKs as possible. Hero placement and spell usage also had to be exact otherwise haunted skeletons would simply overwhelm your defense. I would also advise using haunted gems on bone crushers whenever possible as they provide much needed damage.