I have always said a triangled head with opponent going for kimura is the nastiest place to be on the ground.
Post some other cool ones if you can
A crucifix mount exposes your temple something AWFUL to elbows
a RNC position when the opponent has good control of your midsection and gets your back arched is a surefire way to get choked out. VEry hard to keep chin tucked when your back is arched (try it in your desk chair)
Puerto Rican necktie.
I taught it to Robert Drysdale. 
If You could ever get this dream move to go down....
Our own Big Ben Saunder's Omoplata position is DAMN TOUGH to escape. There is also a neck crank / RNC or face strikes available from this position.IN HISTORY of UFC I believe this is the only Omoplata.
SnapLocally - Puerto Rican necktie.
I taught it to Robert Drysdale.
Im looking for the positions that lead to the sub more than the subs. As far as subs go, this and Rothwell's Choke are bonkers.
Back mount with your hooks in and your hips driving your opponent to stay flattened out.
It's certain death.
T-Ham - Back mount with your hooks in and your hips driving your opponent to stay flattened out.Absolutely, only thing worse is belly down body triangle.
It's certain death.
causing most overall damage? I like Rockhold's mount on Weidman.
most likely to end an MMA fight? I'll go with a prime BJ Penn on your back.
Texas Cloverleaf
See Ryan Schultz vs Chris Horodecki.. That would be awful to be stuck in haha
Rear
Naked
Entry
There is nothing that says dominance like the old RNE. 
Doggy Style......WHAMMY!
Body triangle back control with the opponent belly down to the canvas.
You can chose whether to squeeze the hell, pound their face in or choke your opponent at will with them being completely helpless. Even do all 3 if you're sadistic.
Back control with opponent flat on belly on the floor.
Good luck escaping that.
Back mount with your opponent flattened out is the most dominant hands down. You can submit and hit your opponent, while your opponent can't do any harm to you.
Rickson Gracie style
One thing that bugs me about modern day MMA is that "getting the back" is not as dominant because of the rules. no strikes to the back of the head (particularly elbows) and the gloves that make an RNC that much harder to sink in can really change the whole fight.
It used to be that even if a grappler without good ground and pound "got the back" you were pretty certain the fight was over...now, getting the back typically results in 2 1/2 minutes of trying to snake the arm through for a choke. Being able to pop the guy in the brain stem a few times to loosen him up, made a huge difference.
I'm not necessarily for changing the rule, because obviously fighter safety is important, but just like guys putting 2 fingers on the mat as a defense to getting blasted with a knee, the back position has been castrated.
Gary goo fridge crucifix
(Goodridge)
Auto correct made me lol hard on that one
ApparentlyPaigeVanCan't -VuRam Rod - See Ryan Schultz vs Chris Horodecki.. That would be awful to be stuck in haha
There you go OG