The gorilla arrives onto the battleground, takes his time to analyze, his brain processing faster than a quantum computer, noting all of the elephants weaknesses, his cumbersome heavy body, his propensity to overheat, the sensitivity of his eyes and ears. Quickly, he leaps into action, bounding towards the elephant, he startles it momentarily but the elephant in all its hubris begins its charge. Quickly the gorilla veers course, leaps 20ft up onto a ledge and then onto the elephants neck. Quickly he raises his mighty arms and brings them down like sledgehammers on the elephants floppy ears, then jams his fingers into the elephant's eyes. The elephant shrieks in pain and tosses the gorilla off and into the air. The gorilla's razor sharp intellect begins to quickly search for the next plan of attack while the elephant is blindly flailing about in fury attempting to gore and trample the fiendish ape. The gorilla, while allowing the elephant to tire himself, quickly concocts a new plan, he sprints towards the blinded beast and quickly remounts the bull. Standing atop the leviathan he raises his arms and balls his beefy fists with a mighty roar and brings them down like the hammer of the gods upon the skull of the elephant. With a crack like thunder the elephants skull split asunder and the animal came crashing to the earth like a felled tree. With the gorilla victorious, he showed all who the real king of the jungle was that day.

Either that or the gorilla rips off a tusk and spikes it through the elephant like Vlad the Impaler - take your pick.