What is your favorite form of plank? I am collecting them since I like them so much I will start.

In my new group training class yesterday morning we did a partner plank exercise that I've not seen/done before.

One partner is in the plank position on their forearms, the other person is on their hands and knees focusing on keeping a tight core. The person in the plank position reaches out with one arm and takes the opposite hand of their partner and does a single arm row - all of the time focusing on maintaining a good plank position and to keep the hips even. No twisting the body or allowing a hip to drop!