heady coral
We already have regions of the world with innate temporal instability. As at least one other post has mentioned, those areas are a little unassuming. There are obviously rust monsters coming through and threatening the last reserves of humanity. There are mechanical creatures in caves.
We could use temporal instability as a parameter for spawning a wider variety of mechanical creatures, rust-affected animals, and perhaps even rust affected trees, bushes and flowers. These factors could make those environments more directly challenging instead of passively punitive, and support the existence of novel, unique resources and equipment needed to traverse these spaces.