Re: For all your Nazis-invading-America needs....
Not just Cape York is my understanding. There were apparently a few separate instances all along 'The Top End'. A few works allude to the Japanese Army considering using units of "condemned" soldiers. Basically, just dump them in enemy territory with light equipment, with expectations that they would wreak havoc until destroyed. Given the emphasis given to "high-risk" ventures early on, and Kamikazes later, I suspect that Japanese generals did much more than merely discuss this particular idea.
Besides crocs - add sharks, stonefish, jellyfish, cassowarries, snakes, ferals, vast numbers of mossies, an extraordinary array of other small things that sting / bite (including some PLANTS!), humidity routinely in the 90%+ range, almost impassible terrain alternating between swampy and rugged, the occasional cyclone, etc..
Plus, I honestly doubt that any Japanese commandos dropped off here were prepared for the conditions either materially or in training. Even the "expert" data that the Nackaroos originally had fell far short of the reality - and they had local cooperation, including plenty of assistance from Aboriginals.
Think all the very worst things ever heard about Australia's environment, and absolutely none of the good stuff. Then, quadruple that.