Characters in mythology, literature, movies, etc., who each caused the others death

For something I’m writing I’m wanting a good analogy for internecine “mutually assured destruction” conflict. Who are some characters- or what is some imagery- of two people or beings who killed each other?

Examples I can think of:

In Genesis 3:15 when God is cursing the serpent in the Garden of Eden He says to him

Some see this as messianic prophecy or other symbolism, but I see it- and while I may not be correct it’s an interpretation of others- that is the perfect imagery of what I’m looking for: a human heel crushing the head of a poisonous snake, but the fangs of the snake striking the heel as it does so with the result neither comes out alive.

In literature:

Hamlet and Laertes both die from cuts from the same poisoned sword.

In some versions of Arthurian legend Arthur and Mordred give each other near simultaneous mortal wounds at the Battle of Mt. Badon.

Can you think of any other characters who went down but took their killer with them/killed but were taken down by their victim?

In Norse mythology, Loki and Heimdall slew each other during the battle of Ragnarok.

Is Mt. Badon the same as Badon Hill, where Brave Sir Robin personally wet himself?

Any action movie where the villain mortally wounds the hero, who has just set the countdown on a bomb that will destroy the villain and possibly his Lair of Doom.

Frank Bigelow (Edmund O’Brien) and

Halliday (William Ching)

in the 1950 film D.O.A., in which Bigelow finds that he has been poisoned, and spends his last hours hunting down his own murderer.
And, of course, in the remakes of this, including the awful 1988 version.

The Gingham Dog and the Calico Cat

Hercules and the centaur Nessus. Hercules shot Nessus with a poisoned arrow when he tried to abduct Hercules’ wife. As he was dying, Nessus told the wife to take some of his blood, which he said would restore Hercules’ love for her if she thought it was failing. Many years later, she became suspicious and put it on Hercules’ cloak. He was poisoned by the same poison that had been on the arrow he slew Nessus with, which was so painful he had himself burned on a pyre.

Holmes and Moriarty.

Of course, Holmes came back, but Doyle had every intention at the time of writing that they both died in the falls.

Oh, and another one: didn’t the half-black-half-white guy and the half-white-half-black guy on Star Trek (TOS) pretty much destroy each other together?

The War of the Roses

Thor and Jörmungandr too, for that matter.

Thor and the Midgard Serpent.

ETA: D’oh!

Charles Bronson, “The mechanic” (1972). The professional killer teaches a young assistant about the trade. The assistant, Jan-Michael Vincent, is in truth trying to and succeding in killing the teacher. Bronson has planted a posthumous bomb that completes the cycle.

The, “If you can read this note, you’re going to die”, scenario.

The film Leon: The Professional, with Jean Reno and Gary Oldman.

At the end, professional hit-man Reno is mortally shot by villainous corrupt detective Oldman. As Oldman gloats, Reno sets off a grenade vest he is wearing, blowing both to smithereens.

Alien 3

At the end, Ripley dives into a furnace of molten metal in order to kill the Alien queen that is living inside her body and in the process of emerging.

I feel obliged to point out that the Son of Jord snatched a tiny victory out of that shared defeat. Not only did Jormagundr die first, but Thor managed to take exactly nine steps backward before perishing. Nine is a magic number in Norse tradition.

My ultimate favorite, from Frank Norris’ McTeague is the final conflict between Marcus and McTeague. If you know the book, you’ll agree; if you don’t…check it out!

Romeo and Juliet.

In Tolkien’s works, everyone who has ever been known to slay a Balrog has also died in the process (though admittedly, two of them eventually came back). So far as I know, though, both Ecthelion and Gothmog stayed dead.

You could probably add Claudius to the list. He set it all up and was stabbed by Hamlet.

Fine, but it’s still not enough time to declare a knock-out. The mutual annihilation thing seems to happen all over the place in Ragnarök, I just realized Týr and Garmr do the same thing. Just what are the odds of that happening three times in one day, with all the participants on both sides related by blood?

You’ve never met my family, have you?