The Orangapoid
That had to be the most uphill one on one fight I've seen from the 1930s. I must say, I'm impressed with it. Again and again, Flash escaped from being completely mauled while still suffering from some form or another of abuse. I love the part where the creature nearly bites into Flash's hand, but Flash escapes by slipping his hand from the glove as the creature gets a hold of it. Then immediately following, we get a glimpse of Flash's face bruised as it was. He'd escaped defeat by a narrow margin, but the beating he'd received had still taken such a toll on him that it appeared that he'd only prolonged the encounter. It made it look like it was still just a matter of time before he was taken down and defeated.
The ending was a little goofy though. Flash kicked the thing to the ground and Aura gave away the secret that it had to be pierced through the throat. Just when Flash was about to kill it, the scene shot back to one of the Orangapoid coming through the door and jumps back to an image of him Flash stabbing in a downward direction and the dead Orangapoid lying in the same position it had been. I don't know if they wanted a more climactic ending than him stabbing a downed opponent or if they felt it unsportsmanlike that he'd do such a thing, but it's obvious that they went back and through in that clip to make it appear as if it recovered for another attack. I'll admit, it's more climactic for the creature to get back up and attack once more, only to be speared, but the execution was pretty poor. Still, it does add to the (unintentional) comedy of the serial.