There are some general tactics you can use, but if you know them, then the solution does boil down to guess and check to some extent.
Two tactics that might be useful:
Click here to view the secret text
×
1. The position where you drink a potion is important since you can direct roaches North or South to try to group them up.
Click here to view the secret text
×
2. The wall between the player and the roaches is thin enough that in some situations you can move some of the roaches around even while invisible.
____________________________
106th Skywatcher
