Weights and Multiple Spawn Conditions for Mob Variant Definitions

Currently, mob variant definitions in Java Edition snapshots (as of 25w07a) allow for only three spawn conditions: biome, structure, and moon phase. However, creators cannot "and" conditions together, allowing for, say, a variant to spawn in a particular biome during a particular moon phase. This would allow for greater control over variants added in data packs.

Additionally, it would be very helpful to be able to add weights to different spawn conditions for variants. With this, if more than one variant is eligible to spawn in a location (with same priority), how often each is spawned can be controlled with finer detail. This would be just like how Rabbits spawn, where some biomes have multiple variants, but they do not all spawn equally.

I do love these changes to make such aspects of the game data-driven, and would love to see us creators receive more control!