Although Paldea's Zero Mountain is far from being the world's highest peak, experienced mountain climbers consider it (and, for that matter, the Stony Cliff at its base) the most hazardous, even on the outer side of its caldera. This reputation is justified by the mountain's high population of Klawf, a formidable ambush predator known to drop onto any smaller creatures which walk past, which shows no fear of (or indeed, ability to identify) Man.
Klawf is difficult to spot under ideal visibility, and impossible during one of the mountain's many ferocious storms. It often functions as a load-bearing pokemon, so it is not only those below one who must regard Klawf with concern. Climbers are often stranded or caught in an avalanche when the path they were hoping to take reveals itself as a Klawf's body, then plunges to the surface below. The best surviving accounts of Klawf ambushes come not from the victims, but from those who had to abort their climbs when the Klawf on which they were standing dropped; the snow and the pokemon's own rocky body was enough, at least, to insulate these particular travelers from the fall.
Klawf are not the only crustacean pokemon which one must watch out for on Paldea's mountains; they have been driven from Glaseado by Crabominable, who are far better adapted to extreme cold. Although the two species are known to interbreed in captivity, all known hybrid sightings in the wild originate in excuses made by mountain climbers, who did not want to acknowledge, to themselves or others, that they failed to notice a Crabominable. Skilled climbers have many ways to handle a Crabominable, but there is no shame in letting a Klawf get the drop on you; they are a natural hazard about which nothing can be done.