Glute bridges, both weighted and unweighted, and with a hold and isometric squeeze at the top. Bridging is such an important part of guard and changing positions that you have got to train it like you would a normal "big lift"
You want core strength and stability.
You want pulling strength in general, as you're always pulling on something.
You want grip strength.
I do believe in the big standard lifts for fighters. However there is more to training for fighting than JUST standard lifting. You are in strange positions that you would never find yourself in when playing a field sport like baseball, soccer, basketball. You need to build up the attributes that help you with those strange positions in addition to standard stuff.
Yes 1 arm dumbbell bench is a good bench variation for that, but I would pair it with a lot of 1 armed pulling and a lot of rotational ab work as well.
Working from the top you want a really strong and healthy lower back, as you're going to get cranked on or pulled on. You do want strong hamstrings too, but my experience seems to be that guys don't build either of those, and if they do focus on that they usually let the low back and glutes go on the back burner until it becomes a problem.