This is a plague/darkness aura effect designed to be used on all enemy NPCs in Flicker of Hope (formerly WICK). The game called for something both highly optimized to accommodate multiples on screen when Legiones swarms, as well as being scalable between the very small bugs and very large Mara.
The effect also has an exposed color parameter to allow for a red glow, indicating the player had been spotted by enemy AI.
Stylistically, the goal was to create a look of smokey, billowing darkness, as well as sickness and disease. Color was also added to the effect to increase visibility in a very dark environment. Several layers were used to achieve this look, from basic smokes, to twitching plasma blobs and insect like embers floating around the enemies.
Effect on the Legiones enemy
Effect on Legiones in environment
The effect when applied to a full Legiones AI swarm
Full Legiones AI swarm in game
Effect on the Mara enemy