Because Day 4 of 32 Days of Halloween has typically been a feature on a particular "vs." film, we've gone with two cinematic titans trying to provide the smackdown on one another: King Kong vs. Godzilla.
According to Wikipedia, which is always right, Toho (home of Gojira) wanted to make a Kong movie. So they took an idea for Kong vs. a ginormous version of Frankenstein's Monster (who eventually showed up in one form in Frankenstein Conquers the World) and put the Big G in the Monster's place. Thus giving the Big Scaly One someone new to kick (or atomic breath) the crap out of. The rest, as they say, is history. Giant screaming rubber-suited history.
We started this whole Vs. mess the first year with Dracula vs. Frankenstein, then a round-up which included the aforementioned Frankenstein Conquers..., then we couldn't resist Ninjas vs. Zombies and then Tucker & Dale Vs. Evil, which is finally getting released. Enjoy!