Screentones
A collection of screentones.
Many are taken from Mangadex, but reformatted into a format that makes it easier to view; there are some additional ones here as well.
Many of these screentones tile; the version you download will be a very small image, and you are expected to make a pattern out of it in your editor.
It may additionally be helpful to browse the Clip Studio Paint asset store, which contains many commonly-used screentones.
Animals Bubbles Dots Flowers Foliage Glitter Hatch Hearts Herringbone Lace Lightning Lines Pentagons Random Stars Stars (Persona 5) Swirls Tartan Text balloon impact lines