This one is real bad as you have to protect it for 11 turns and you have like 40 things to fight with multiple access points and half way through the map changes and suddenly it becomes more open, and two rather strong units are among them and multiple units can lower your defense after combat. Plus I'm on Hard and Classic, so my units die like normal.
For some reason I just lose even though things go so well, just lost again right at the 2nd to last round I had to go through. One of the stronger ones somehow did more damage a turn later, which made no sense and suddenly math wasn't on my side. It was going so so so so well.