One-leg Guard
At our meet up, Leo taught me a guard that Marcelo showed at his last seminar. He calls it the “one-legged x-guard” since it ties into the normal x-guard game. It’s a really strong position for sweeping and has obvious leglock potential.
Marcelo taught it as what he has been doing now that people are wise to x-guard and will prevent him from underhooking their leg to avoid it. He’s now also playing a guard game that’s based on overhooking the leg (which is easier to do at a distance) and wrapping their trapped leg with both of his.
I’d seen Marcelo use it successfully on black belts, but thought it was just improvised, but it turns out he really does play like this on purpose. You can see a similar sweep at about 1:00 in this video.
Here’s how it goes:

While playing open guard of some sort (probably sitting guard and trying to get x-guard) overhook their leg as you kick your left leg through the middle. Your right leg is hooking behind their far knee.

Wrap your left leg behind their leg and step on their near hip. Your right hand pushes on their far knee to keep it away.

Then bring your right foot to the same hip. Or you can hook under their thigh like you’re doing a leglock.
This is the main position. Keep your knees pinched tightly around their leg and push on their hip with both heels.
As in x-guard, grab their far ankle as soon as you can.
To sweep, straighten your body and shove your heels into their hip to push them back. This may be enough on its own to sweep them. Holding the ankle too makes it all the stronger.

After the sweep, there is an obvious ankle lock or you can take out your feet and come to your knees.
Just tonight I used this successfully several times in a row on a blue belt with a 90 lbs. (or more) weight advantage. He tried to come down and crush into me but the power of both my feet on his hip was enough to push him off and straighten his leg. As with the ankle grab x-guard sweep, I couldn’t reach his ankle at first, so I tried to sweep without it, which he countered by bringing his base closer so I could grab his foot. Then I swept again and down her went.
I ankle locked him after the sweep both times. He tried the normal leglock escape of kicking his leg through deeper, pulling my lapel, trying to sit up, etc. but because both of my feet were on his hip, none of this really worked.