4Game

(numbers listed are just for example.)
(for int n >= 0, float a == 1.5, float b == 0.15)

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Allow mobs with more than two stars to spawn, with a simple algorithm for star number determination:
15% (b) chance for a mob that is going to spawn with n stars to instead spawn with n+1 stars, recursive

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3 offensive star types and 3 secondary star types, rolled independently of each other:

Gold stars – extra damage, each star multiplies mob damage by 1.2x (0.8a).

Green stars – extra attack speed, each star multiplies mob attack speed by 1.2x (0.8a).

Blue stars – extra attack range, each star multiplies mob attack range by 1.2x (0.8a).

Red stars – extra health, each star multiplies mob health by 1.5x (a).

Silver stars – extra movement speed to the starred mob and all mobs within range, each star multiplies mob movement speed by 1.1x (about 0.73a).

White stars – extra vision range to the starred mob and all mobs within range, each star multiplies mob vision range by 1.2x (0.8a)

Each star multiplies reward drop ranges (minimum and maximum) by 1.5x (a).

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And possibly 2 other star types that don't roll multiple times:

Black star –  fixed 1.5% (0.1b) chance – rerolls all stars on a mob 5 times and takes the highest number of each star type, hides all stars except the black star.

Purple star – fixed 1.5% (0.1b) chance – multiplies reward drops by 3 (2a), mob always flees when damaged, any gold stars are converted into additional red stars, any green stars are converted into additional silver stars, and any blue stars are converted into additional white stars.