This movie shows how my thinking Particles flak asset works. All animation is totally procedural. Everything except Fume FX is one thinking Particles setting.
UFO are generated in the volume of sphere and fly around in the sphere. UFO follow "follow particles". Follow particles reflect on the sphere surface by intersect node to get sphere's normal. UFO follow those particles using position follow node with high laziness.
Gunners aim nearest UFO using PSearch. When gunners shoot flak gun, if bullet is in a certain distance between UFO, Bullet explode like proximity fuse. Distance is decided random seed. When bullet is close enough to UFO, proximity fuse hits then UFO starts falling down.