Mass Hydras? Well, since this thread is based on theorycraft, here goes nothing:
With Protoss. I would have Photon Cannons obviously, and to counter your drog effectively and safetly, I would cast a Mealstorm here and there so that your overlords are stuck in cross-fire. If you try to unload them, I would have a Psi Storm ready to fry them. Since I've seen you do this little strategy, Azrael, I know how to best counter it now, I'll admit you got me good with it the first time, but since we both suck, it was a fair game.
Creative? I could just Mind-control your overlords. Your units are now mine.
Terran: Siege Tanks with Goliath/Ghost support, Science Vessel. Siege Mode Tanks would siege the enemy while the other troops protect them. This one's easy to beat, so whack at it.