More, please. This is fun to read.
The two set up, scouting out the local lairs. Many of the ones in the area were home to great and terrible beasts, ones that the wanderer judged too great a threat to deal with in their current state. It was during their first few nights in the harsh desert that their first trial occurred, not in the form of a great beast but mere wildlife, starving dingos and vultures. The human suffered no great injury, but...

While battle-scarred, the serpent woman was otherwise unharmed in the end. Their scouting continued until they reached great expanse of desert, with signs of greatly disturbed sand, and evidence of the wildlife avoiding the area entirely, even vultures preferring not to fly over the region.
With a great tremor within the earth, their threat made itself clear. A massive, slithering chitinous beast with armored plates surrounding many segments, and a maw filled with countless massive, dagger-like teeth. The great wyrm. The eternal thing.
The adventurer ordered his companion to hang back, an order she was eager to follow, as he met the beast on sprawling sands, the creature charging across erratically. Given its size it was fortunate for him that the beast couldn't dig or move beneath the sand to attack from below, preferring only to burrow to gain shelter from the sun.
Jab, backpedal, exploit every single gap in the massive plates. Crudely-knapped stone met little resistance whereever it struck these vulnerable spots, the human clambering onto the great beast to jab into the segement that he guessed was the creature's head. That alone seemed to make the creature thrash erratically, yet undeterred even when became clear he tore directly through the closest thing the creature had to a brain.
When its flailing about forced him to resume his cautious strikes, another jab between plates revealed a similar reaction, this time the creature's movements slowing until, moments later, it lay dead before him, coiled in a massive circle around him, having been poised to attempt another frantic strike when he hit his mark.
With crude armor of stiff chitin and hard bony plates, and a massive tooth of iron-like hardness affixed to a spear shaft, the adventurer continued onward, companion in tow...