The yrthak was one of the standout new monsters from the 3.0 Monster Manual. It’s also one of the rare cases where I prefer the original D&D art to the Pathfinder version. Don't get me wrong—Mike Corriero’s pteranodon-like yrthak from the Bestiary 2 is really well done and makes sense from an evolutionary perspective. But something about the original yrthak—scrawny, eyeless, with a too-large, gulper eel-like mouth—really spoke to me. It called to mind all those shrieking dragons from old Hanna-Barbera cartoons like The Herculoids, and that imagery is too deep in my DNA to ignore. (Which yrthak you prefer is, of course, up to you.)
I spend a lot of time in these posts talking about how X monster or Y race is more interesting than it first appears. But yrthaks are a throwback in more ways than one—to the good old days when a monster just needed to be a monster, preferably with a single unique special ability. Yrthaks don't form societies or gather followers or do anything more complicated than hunt. They live in inaccessible canyons, badlands, and escarpments, swooping down to terrorize the plains with their sonic lances. They exist to populate the random encounter table and surprise your players with their odd abilities. They are simple and simply violent, and I think that’s simply fine.
On the Dark Isle of Telosan, yrthaks have almost completely replaced the native pteranodons. Instead of diving to catch their meals, the yrthaks stun fish with explosive blasts and then skim them off the top of the water with their needle-like teeth. Fringed with white fur, glacier yrthaks are resistant to cold but loathe fire magic; they are known to use sonic lance blasts just to put out campfires. And Tiempran skyships all come armed with yrthak bells or gongs to drive the creatures away.
A yrthak captured a bard, and found itself captivated in turn by the half-elf’s melodious piping. Now the two rove as bandits, tormenting the cliff folk of Highhall and Red Sands. Capturing the pair will not be easy, as they travel frequently and rig their hideouts with deadfalls and avalanches that can be triggered by sound alone. But killing them would be equally unwise, as the half-elf is the son of a very prickly elf chieftain who will go to war over any insult to his children, even his half-human bastard.
Sonic attacks are one of the few types of energy that affect nearly all fiends. Certain celestials have taken advantage of this fact, training yrthaks as mounts for aerial assaults. The reptiles are too wild for the taste of most angels and archons, but the lower orders of agathions and azatas (especially vulpinals and bralanis) take great pleasure in blasting demons and devils with their yrthak steeds’ sonic lances.
—Pathfinder Bestiary 2 290
Peter Bergting’s “The Ecology of the Yrthak” appeared in Dragon #352 (and featured a kaiju yrthak to boot!). But the real reason to get that issue is for the in-depth look at China Tom Miéville’s world of Bas-Lag (including monster stats!). It’s also got a nice quick-and-dirty approach to warforged, a look at the Isle of Dread’s natives (both articles from Nicolas Logue, incidentally), and two Aztec deities. Definitely a classic of the latter-day Dragon issues, and well worth your time.