created a new effect today, the KawaseBlur (also added to the first post).
The Kawase Blur is designed to mimic a gaussian blur at much better performance.
It's supposed to be used with multiple passes.
To avoid artifacts use the following kernels depending on how strong the blur needs to be
2 pass = 0.5, 0.5
3 pass = 0.5, 1.5, 1.5
4 pass = 0.5, 1.5, 1.5, 2.5
5 pass = 0.5, 1.5, 2.5, 2.5, 3.5
7 pass = 0.5, 1.5, 2.5, 3.5, 4.5, 4.5, 5.5
10 pass = 0.5, 1.5, 2.5, 3.5, 4.5, 5.5, 7.5, 8.5, 9.5, 10.5
(for example for the 4 pass blur you add KawaseBlur 4 times and the set the kernels for each effect in that order) You can also try other sequences (like 1.5, 2.5, 3.5, 4.5) but you might get artifacts.
https://www.construct.net/en/make-games/addons/1110/kawase-blur
example of the effect used as a background blur in my game