I feel like you have the potential to make a really cool Steven Universe mod, I have asked a few mod creators before like 01 studio (no hate they're really busy).

Suggestions:
Different gems with cool weapons, abilities, fusion and more.
Injectors: placing them in the map tiles will spawn random gems with varying chances depending on the gems strength, or special outcrops/ore deposits for certain types of gems.
Shapeshifting: replicating other mod characters appearances with color differences.
Gems would also have active and unactive/poofed forms of course.
If a gem cracks they will slowly lose limbs or mutate in weird ways until shattering in a couple of minutes.
Gem shards: they cant do anything on their own unless healed back together, or unless they are forcefully fused.
forced fusions can only regenerate the limb that they represent, so when a gem shatters they will become 6 pieces, head, body, 2 arms, and 2 legs, and using forced fusion they can become hybrids of many gems.(you can check or change the type of gem piece in the context menu).
gem doors with interiors based on the gem type would also be pretty cool.

Due to indeepj's comment I have now considered the fact that you could make a giant head cluster so I have decided that when all the shards are the same the gems become a giant multi-colored version of that limb