When I un/burrow the Pests they loose all their cummulated attack. Is that a bug or a feature?
This makes it sound like you're re burrowing after the first unburrow, post SoPa discarding. You dont do that. Play a pest, fractal, play all the pests but one for refractaling, burrow them, play sopa, wait as many turns as you can. Weaken the HP down with siphons/ remove shields before attacking of course.
Edit: Also, you might wanna add the [OTK] tag to the title. The possiblity to OTK is
very likely, even without siphons or otherwise.