Getting chased by Grapploct was a real highlight (it's so intense how it goes from resting to GONNA GET YOU) but honestly i have no idea how someone is supposed to get hit by the carkol unless you are actively backtracking. I didn't even know there was a carkol there until later, i just throught it was timed scenery of an actual coal kart that rockets off as you approach.Sword and Shield's routes have gotten a fair amount of criticism for being short and linear, but one thing I love about them is how they integrate wild Pokemon as obstacles. The one I remember most fondly is encountering the over-leveled Carkol in Galar Mine, but other encounters like the Grapploct that swims after you, the Falinks that march from one end of the map to the other, and the Galarian Stunfisk that act like actual bear traps were also really memorable. I'm hoping this concept is iterated on in future titles since it has multiple applicable uses, like challenging the player outside of battling, and making these locations feel more unique to Pokemon.
Another good one, though it's not as "active" an obstacle as the others are: the beartic on the final route. It always spawns right next to the final hill and, you know, being chased by a giant polar bear? Low key terrifying, at the very least.