Spell particles

Bedrock draws the swirls of potions and status effects with several particle effects, where Java Edition has the entity_effect, effect and instant_effect particle types. Each effect takes its colour from variable.color, a struct with .r, .g, .b and .a, which no file assigns, so the engine sets it. Observed · the vanilla spell effects of bedrock-samples v1.26.60.5

The effects

Effect	Emits	Variables read and never assigned
minecraft:mobspell_emitter	one particle, once	color (all four channels)
minecraft:mobspell_ambient	one particle, once	color (.r, .g, .b; alpha fixed at 0.4)
minecraft:arrow_spell_emitter	one particle, once	color
minecraft:mobspell_lingering	π × cloud_radius² × particle_multiplier particles, once, over a disc of cloud_radius	color, cloud_radius, particle_multiplier, cloud_lifetime (the emitter’s active time)
minecraft:splash_spell_emitter	100 particles, once	color, color_brightness, is_vertical, splash_power, splash_range

Observed · the vanilla particle files of bedrock-samples v1.26.60.5, Molang names compared case-insensitively

When each starts

splash_spell_emitter is produced by splash potions. mobspell_emitter is emitted by players with non-ambient effects and is listed for area effect clouds from lingering potions too; mobspell_ambient by players with ambient effects (a beacon’s or a conduit’s). arrow_spell_emitter floats off tipped arrows and trails behind spectral arrows. evoker_spell is an evoker casting a spell. Sourced · Minecraft Wiki, Particles (Bedrock Edition)

mobspell_lingering’s variables are named for a cloud (cloud_radius, cloud_lifetime), which points to the lingering potion’s cloud. Inferred

How often does the engine start mobspell_lingering, and with what multiplier and lifetime?

One start of the effect emits its particles once (instant rate, a single emitter lifetime), so a cloud that shows particles for its whole life must start it again and again. Its count, π r² with a multiplier of 1, is the number of particles a Java Edition cloud spawns each tick, which suggests one start per tick. Inferred The Minecraft Wiki names mobspell_emitter for the clouds instead, and gives mobspell_lingering no description.