I have recently tried to look for submissions a lot more from the bottom since they probably are one of my weaker points. I've been trying both guillotines and loop chokes from the bottom. For example Marcelo seems keep his opponent's cautious of dropping their necks too low because of his guillotine from hell. Opponents mind their necks and end up getting swept. In Marcelo's case this happens often with the hook sweep from butterfly guard.
As I don't have a good understanding of guillotine mechanics I've started experimenting with the loop choke from Z-guard. Today I managed to catch a seasoned blue belt off guard with it. I noticed that just like Marcelo's guillotine and hook sweep, a Z-guard look choke seems to work well with the basic Z-guard push sweep (hold the sleeve, push with ankle to armpitholding collar or fabric around the knee).
We also experimented with a version where the choking collar grip is made palm down instead of palm up. This makes slipping the other hand below the elbow slightly easier