Out of all three movies, this is the darkest one in the franchise.
There are a few jump scares.
Sonic tried to enter a sphere-like laser over GUN H. Q. and says he won't make it, referring to him being injured severely.
This film is much darker than the first two.
When Shadow returns to a base that is now defunct, he gets nostalgic because it is where he meet his friend Maria, and he remembers all the heartwarming times he had with her. This scene is poignant.
Despite the poignant/dark film, there's some brash moments, though mostly light-hearted mood of the film balance them out.
This movie is more let-go/dark than the other 2 sonic films.
Sonic's super sonic power runs out, tails then jumps out of a space ship holding his breath to rescue him, then in one scene burns burns up a bit from the space atmosphere, this may be upsetting for some viewers.