Rex walks through the tall grass and flowers, cutting through the mist, and heads to the castle.
Many of the mutated animals are avoiding these tall grass and flowers due to the fact that these mutated plants are emitting a scent that can only be sensed by animals, the scent is not horrible or anything but it dissuades them from going through the open place.
Something that is pretty convenient as the place has already a built-in defensive mechanism.
Although the mutated animals are not a problem thanks to these mutated plants covering the entire open place, the cursed creatures are the ones to look out for as they are not affected by these mutated plants' scent.
This is why Rex and the others have been trying to clean the cursed creatures in this forest.