To remove the particles, open the folder with the game, go to Resources and search for the file square.png . Next, open this file via Paint, fill it with black color and save it.
In order to remove the trail, do the same with the streak_01_001.png file. (P.S. don't forget to select the most standard (first) trail in the game).
Congratulations! You've removed the particles and the trail!

YouTube: WXST [GD]
In-game profile: wxst