In one word: “inventive”.
The visual space of the movie is interesting. It is a mixture of the real (Jean Kayak and other human characters), the cartoonish real (the cardboard cut-outs, animals who are animals-in-constumes), and the cartoonish (the animations and VFX). As a result, the visual space is incongruous. This becomes a preconfigured ground for gag comedy. Additionally, the incongruous visual space is never disconnected, the real and the cartoon are mediated by the cartoonish-real.
Gag comedy is formally structured through incongruity. A normal situation is resolved absurd, perhaps the situation is ludicrous to start, and demands more ludicrous resolutions. In the film, there are ridiculous systems. These are unusual situations, sometimes hinging on bare contingencies, with a consistent logic to them. For instance, there is the bird that pecks at any head, snow or flesh, appearing beneath Jean Kayak’s hat the moment he whistles, even from the far side of the forest. There is also the inexplicable shift in the direction of the snow squalls, which resolves itself when Kayak turns his back to the wind, shielding the fire with his body. The accretion of ridiculous systems connected logically permits Kaya’s movement through the Campbellian hero’s journey.
The possibility of gag cinema is the invention of new concrete gags. And Hundreds of Beavers successfully lives up to that possibility.