I thought he looked at the reflection on his shield himself, so he could see her without turning to stone, and fought backward.
Indeed. Since there doesn’t seem to be a straight up “Tricked the giant into falling into the volcano” type answer, I’m cool with letting the definitions be hazy and people responding whatever they think broadly fits.
This is indeed what is the usual form of the myth. Although in a lot of ancient artwork Perseus is depicted as simply not looking at the Gorgon he is supposed to be fighting, as if fighting “by touch”, not needed a reflective shield to keep him from looking directly at the monster.
This is a modern wood carving based on a temple image:
Here’s a vase with Perseus cutting off the head of a Medusa-Centaur, very definitely lookng away
https://www.theoi.com/Gallery/R47.2.html
Here he is on another vase, looking away as he cuts off the head of a “beautiful” medusa
Here’s a pretty famous one in the British museum showing his head averted
Such images, with Perseus looking so clearly elsewhere than at Medusa, may have given rise to the idea of his having not to look directly at her. You’d be hard-pressed to find an ancient image of Perseus looking into a mirror to cut off her head in classic art.
Greek mythology has numerous examples of horrible monsters overcome by subterfuge, including the man-eating mares of Diomedes, and the Colchian Dragon which guarded the Golden Fleece.*
*Jason killed or at least neutralized the dragon with the help of Medea, who put it to sleep. Afterwards, Jason went on to found a chain of delicatessens.
I looked at a couple accounts just now and it looked straight forward. Hercules is supposed to get the horses so he gets some guys together, they take out the guards and drive the horses onto the beach. Hercules needs to fight someone else so he leaves the mares with a young companion who gets eaten. Then he brings the horses to Eurystheus, completing the task.
Hah.
“Heracles (Hercules) defeated these monsters in his eight labor. He fed Diomedes, their master, to his own horses and while they were occupied with their human meal, Heracles found the opportunity to bind their mouths shut.”
Trickery!
Wotan and Loge trick the shape changing Albriech into assuming a form so that he can easily hide and spy on his enemies. Albreich changes into a toad, and is tied up and made to give up the rhinegold.
You can’t get much better than Jack the Giant-Killer. There are a lot of different tricks by which he murders giants, but here’s my favorite:
And, of course, the Brave Little Tailor kills giants with trickery:
Shouldn’t the cat’s tail be fluffed up?
If you’re interested in “Defeated”, not just “killed,” the Egyptian gods defeated one of their own through the trick of getting that one completely wasted:
Since the OP isn’t interested in consumer media examples, I guess the ending of “Tremors” is right out.
If a bully counts as a “monster”, there’s a story from Turkey about a character named Nasreddin Hodja who defeats a bully by claiming to be stronger. Specifically, “I can throw something farther than you can.” The much bigger bully laughs. Hodja hands him a handkerchief. Turns out the secret is to tie a knot in it and then throw. The bully leaves town.
Although in the Harryhausen movie Jason undoes the stopper on his single vein and lets out his ichor (or whatever that’s supposed to be), I don’t think that happens in any version of the myth. In one, Talos himself is responsible, scratching his heel on a rock and breaking the vein open.
Only one version , the cited one from Apollodorus’ library, has Talos dying of trickery, and that’s not the dominant version.