One thing I've been working on is a variation system for Pokémon, inspired by Magikarp Jump and Pokémon Stadium. Here's how it works.
Each Pokémon will have 4 variables, each with 8 normal options. This gives us 4,096 unique variants for each Pokémon. For use in my TTRPG, variations are decided with a d20. Options are broken into groups:
Base — This is the option which is present in the original design. 20% (1-4) of the time, this option is picked.
Common — There are 3 common options, each at 15% (5-7, 8-10, & 11-13). These are supposed to look closer to the base design for the colour variant, like a tan Rapidash.
Uncommon — There are 3 uncommon options, each at 10% (14-15, 16-17, & 18-19). These are further away from the base colour.
Rare — This is a mere 5% (20) chance. This is the most different to the original colour. For example, black Rapidash.
Each variable is rolled separately, meaning each Pokémon is most likely to have the base variants, but is also likely to have at least 1 variant that isn't the base.
The base colour of the Pokémon would affect the major colour of the body. Each Pokémon is grouped together based on shared attributes. These Pokémon then use the colours of the group as the available options. Currently the groups are thus:
Metallic — silver, steel, platinum, cobalt, gold, brass, black iron, and pearlescent
Equestrian — tan, cream, brown, red, white, light gray, gray, and black
The specific colours can be spread differently between the base, common, uncommon, and rare options based on the different species. Also, Shiny colours always override the base colour.
Patterns are given individual names to make them easily referenced. Both the colour and pattern will show on the Pokémon's summary (black-spotted for example). The pattern styles will be shared between all Pokémon (although I'm open to this changing):
Only colour and patterns are available.
I think having special patterns that only appear during certain times of the year would also be fun. These would be in addition to the 8 variants here. For example, a spooky pattern for Halloween, or a lovely pattern for Valentines day. They would override the patterns when generating the Pokémon in game. I also would like Magikarp and Feebas to have a bunch of extra patterns.
These are species specific variations. Stuff like different types of horns or scars. It's very dependent on the specific Pokémon.