Croaker's Legends
All of the listed examples were done in one try without saving and redoing any mistakes I made during the game, and each level is done without vets from previous levels. This way you will understand the strategy behind the level and not just the troop control. Also, it will show you what can happen if you're not careful.
In all of the solo levels, especially on Legendary, you are completely outnumbered. The trick is to use your head and the terrain to outsmart and outplay the AI. Formations and terrain are of extreme importance and the childrens game "Rock, Paper, Scissors" is a good thing to keep in mind while playing.
The single most common reason for a failed co-op is bad Dwarf handling.
Never throw a bottle into your own troops. Do your damage and get out of the way. I can always tell I'm going to lose a co-op when the Dwarf starts tossing bottles around for fun. Sloppy Dwarves do not a Legend make.