Whimsical burrowing.
The AI will practically burrow any time they can, and only unburrow at some absurd point when they think it will finish you off (even if you were already going to be finished with their burrowed ATK, and even if the burrowed creature has no ATK, ie Devourers).
They would have to have some kind of risk assessy-type thing going on, like, burrow against Fire user, Burrow if Eagles Eye is floating about, but maybe not if they have 4+ def eg Elite Shrieker.
Stuff! :]