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Most of the following features are stored in "assets\minecraft\optifine\random\entity" folder in this pack, can try removing the ones you don't want. 
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- brown bear
in any non-natural spawning biomes for polar bears

- black & white, brown cow
random variants, warm biomes tend to have more brown variants

- slightly darker green creeper
random variants

- brown frog
random variants for temperate biome frogs

- swapped warm and cold biome frog variants
rename the frog textures in the "assets\minecraft\textures\entity\frog" folder if you want it reverted back to vanilla

- dirty hoglin
random variants

- muddy pig or hairy boar
random variants, colder biomes tend to have more hairy boars

- topless piglin
random variants

- topless zombified piglin
random variants

- black skin sheep
random variants

- hoodless or topless stray
random variants

- tarantula spider
random variants

- black & yellow cave spider
random variants

- orange squid
random variants

- greener glow squid
random variants

- brown sea turtle
random variants

- dark gray and brown wolf
random variants, colder biomes tend to have less

- topless zombie
random variants

- topless drowned
random variants

- naked husk
random variants

- brown chicken
random variants

- baby chicken
baby chicken has yellow feathers/fur

- gray dolphin
random variants

- darker silverfish
random variants