There are some combos that's horribly efficient. The habit together with the yum heart makes you able to refill health (almost) as fast as you lose it. Anything flying together with lots of bombs makes killing mother a piece of cake, since you can just fly around in circles and bomb the doors. Technology and the ouija board is crazy effective at killing a lot of things.
I really hate the one that gives you explosive shots, though. While it's effective, and lets you check for hidden doors, dammit is it impossible to hit stuff chasing you, or moving fast.