The shader comes from a water one that I adapted, it wasn't easy so thanks you !
I think your remark is spot on with the difficulties to differentiates ennemies. It's a point we would have dig more if we had time, and the overall game design. We added the blood moving from the ennemies dirrectly to the gauges and the 0.5 blood type animation where an ennemy dies to remedy this, but we could have done more.
Thanks you for the feedback, have a great day :) !