By far my least favorite stage to three medal was campaign stage 10-5. That's the stage where a normal pest fight was parked in an S-shaped area that required one squad to be WAY faster than any of the others in order to reach it in time on top of needing at least two randomizer panels to direct the squad down the right path towards said pest fight.

It wouldn't be too big a deal for me to clear now that I have multiple allies with 700-1000 speed along with the speed down trait on my Knights as needed, but MAN did I burn a lot of stamina all those months ago.