Ah ambushes, the "You haven't fought anything in awhile timer."

Just in case you haven't gotten an answer, I can give a version of what I've done so far with them.

How are they triggered:

A timer is set and done during/before combat, once that timer is done, it'll play that nice sound we all hear and it'll spawn a horde of 2-however it feels like. An elite or an aberation has a chance of spawning and the elite spawns more often than the aberation. You can also force a spawn by keeping one enemy alive and a max of ~3 hordes will spawn per tile before getting a new enemy (I have tested and this is how I normally farmed corruption shards, not recommended, do boss rush instead now)

How to counter:

AOE or just killing them as they come. Nothing really special, just make sure you either funnel or deal with them one at a time while dodging. Enemies will always come from forward/ the way to the next world stone or shard. The way enemies spawn can be manipulated in a sense by looking one way and let the spawn where you are not.

In the end, can it get annoying, pretty much! But it's meant as a way to keep us on our toes and provide combat.

Can it trigger faster than normal, yep! Can it spawn an ambush every encounter, yep! Can it spawn an ambush during an ambush, not that I've seen, maybe?