I’ve been using this combination superman plank finisher as the finisher for my core workouts lately. (A finisher is an exercise meant to finish you off in essence, though I’m still not going to failure in it.)
This is a combination of one arm, one leg superman planks on each side followed by a regular superman plank.
I cover more of this type of training inside Strengthen Your Structure, a guide mostly about carrying heavy weights in various ways, but also covers some bodyweight leverage exercises such as this one.
But you can find a lot more on ab training inside of The Ultimate Guide to Bodyweight Ab Exercises.