Blazon: Argent on a pale vert between two flanks gules, the dexter charged with five trefoils in pale and the sinister with a chain in pale, a triple mount in base and a stone hut of the field
Donnersbachwald technically no longer exists, as it was incorporated into the municipality of Irdning-Donnersbachtal in 2015. I’d assume that the mount refers to the local geography, which is extremely common for municipal arms. The vert and argent tinctures may be a reference to the Styrian arms, but that’s only speculation. Unfortunately, I’ve got nothing on the stone hut (or Kuppelbau, as the German blazon has it). My guess is that it’s a distinctive archeological construction in the region, which is also a pretty common motif for cities and towns, but I can’t find any mention of something like that. And if you’re wondering why I’ve called the charges on the sides “flanks,” see here. TL;DR it’s a charge specific to German heraldry, and they’re not the same things as flaunches.