Glad you like it! And true, I'll move the reset button further away.
Every GameObject with a sprite has a child holding a "blank texture", so the blood stays on-grid and moves and rotates with it. Collision is enabled on the particle system-explosion, so each drop reports where it hit and writes a pixel at that point. Repeat hits on the same pixel darken it, and once it's full the drop keeps "moving" to the next free pixel below. Thats basiclly it :D