Walkthroughs for custom maps.

What needs to be done to consciously replicate this effect? Why are the Crystal Dragons standing still? https://www.youtube.com/watch?v=icXZ--m_nvk&feature=youtu.be

This is because, due to the quicksand, they can only move one cell at a time, and then the AI often decides not to move at all.
The AI, as it were, loses sight of the target it can reach, so it goes into defense and stands still.
To replicate it, you probably need to surround the enemy stack with quicksand so that there are more than a certain number of turns until the target.