Perhaps I forgot a few. So here’s Appendix II, 19 years later, with knowledge of Books 6-7 of the Potterverse. Team Prydain is still winning.
Achren vs. Bellatrix
The former queen and evil enchantress of Prydain vs. the worst (or is it the best?) of the Death-Eaters.
You might think about this as a straight-up fight with spells and all that nonsense. You’d be wrong.
Bellatrix defeated quite a few named wizards in Books 5-7, and murdered Sirius and Dobby. On the negative side, though, she was just a speed bump for Dumbledore while he dueled Voldemort, her cruelty is tempered by fear of her master, and as she was finally smoked by Molly Weasley, she literally was killed by the power of love.
Achren is not someone you can kill with the power of love. She once was more powerful than Arawn, and never forgot it. Even his seizure of Annuvin did not stop her quest for power – and neither the destruction of Spiral Castle, nor the crumbling of Caer Colur. She was cunning enough to retreat to Caer Dallben to lick her wounds and do the dishes, clever enough to switch sides and aid the companions – and calculating enough to get her revenge on Arawn whilst seemingly powerless. She lived on her terms.
Bellatrix was ever a follower. Achren was always a queen, even in death. Bellatrix will serve her purposes, one way or another.
Advantage: Achren.
Morda vs. Dolores Umbridge
Who’s the vilest from each set of novels?
Morda, the lich murderer of Eilonwy’s mother, is up there. And even in a field including Voldemort, Umbridge has no real competition. If these two were ever once human, it was long ago.
Unfortunately for the winner of Hogwarts’s Worst Administrator Ever award, finding the hiding place of Morda’s phylactery requires having a loyal and inquisitive crow, and Umbridge loves nothing save herself.
Alas, she will spend the rest of her miserable excuse for a life as a blind worm.
Advantage: Morda.
Coll vs. Remus Lupin
Outwardly cheerful, helpful, wise, and damn good in a fight, but they’ve got some dark secrets, and they ultimately fall in battle – the fate of many a good man.
But the veteran Coll is too smart to tangle with a wizard, and after a lifetime of concealing his nature, Lupin tends to act only in defense and only if necessary.
They will circle each other for a bit and then agree to withdraw.
Perhaps there will be an exchange of chocolate and turnips.
I guess we’ll never know.
Advantage: Tie.
Glew vs. Argus Filch
Little men with cats and a grand ambition to be big; if only their actions matched their ambitions.
If Glew is still a giant, no contest. If Glew is not a giant (and Llyan is not involved) Filch’s casual cruelty, janitorial longevity, and squib resentment might win out. It wouldn’t be pretty.
Mrs. Norris has no effect either way.
Advantage: Filch.
Adaon vs. Cedric Diggory
While not quite adults, they are role models for the protagonists, and in storytelling terms, they serve the same function – guilt. Taran feels his decision to pursue the Cauldron got Adaon killed, and likewise, Harry feels responsible for Cedric’s murder. They are both wrong, of course.
Cedric is a strong young wizard, but he only “wins” the Tri-Wizard tournament with Harry’s help, and Pettigrew kills him in an eyeblink.
Adaon would know of any conflict with Cedric the night before it occurred, courtesy of the powers of his iron brooch. He turns events to his favor, perhaps by avoiding direct conflict altogether. Cedric’s failure to escape the trap at the end of the tournament is a clear sign he has no defense.
Advantage: Adaon.
Morgant vs. Gilderoy Lockhart
One is a warrior king that has saved Gwydion’s life several times. The other is really good at, ah, memory charms. But they’re both the turncoat antagonists of the second book of each series: Morgant betrays the companions for the power of the Cauldron, and Lockhart is ever anxious to preserve his fake reputation, even by stealing the memories of innocent children right when they’re… wow, those two books kind of line right up.
So it seems Morgant and Lockhart are fated to do battle.
Alas, Morgant has a large and loyal war band that always follows him around. He captures the companions (and Ellidyr beforehand) with a single verbal command. I see no reason this would go any differently. Without his wand, Lockhart is helpless (and he’s not very good with it, as Snape demonstrated).
First into the cauldron.
Advantage: Morgant.
Pryderi vs. Lucius Malfoy
The quest for power and station rarely ends well. Pryderi betrayed the Sons of Don for empty promises from Arawn and met his match via whatever mystical voltage the Book of Three puts out. Lucius Malfoy played both sides as well, and only escaped a second stint in Azkaban after switching for a final time against Voldemort to protect his son.
The only difference, perhaps, is that Lucius is far more cowardly, and that makes Pryderi, armed with a dagger from the hand of Arawn himself, unstoppable.
Advantage: Pryderi.
Hen Wen vs. Sybill Trelawny
I don’t recommend fighting with an ocular pig. You’ll get muddy and the pig will have seen it coming.
The physical realm seems completely unsuited to this contest. So let’s get serious for once and look at the prophecies themselves.
Sybill’s is this:
The one with the power to vanquish the Dark Lord approaches. Born to those who have thrice defied him, born as the seventh month dies, and the Dark Lord will mark him as his equal, but he will have power the Dark Lord knows not, and either must die at the hand of the other for neither can live while the other survives. The one with the power to vanquish the Dark Lord will be born as the seventh month dies.
Whether this prophecy concerns Harry or Neville or someone else is not answered for some time, but it is not a hard read. So, points for comprehension, if not style.
As for the pig, Dallben asks her where to find Dyrnwyn in The High King:
Ask, sooner, mute stone and voiceless rock to speak.
Completely useless… and completely accurate, and more concise, too.
However, that’s not all. Dallben then attempts to get clarity, which results in the letter sticks shattering, but not before Hen Wen delivers the goods:
Quenched will be Dyrnwyn’s flame
Vanished, its power.
Night turn to noon
And rivers burn with frozen fire
Ere Dyrnwyn be regained.
I don’t know about you, but something epic is about to go down.
Advantage: Hen Wen.