Gems
Gems make one type's attacks hit harder. They start dropping once you have the Gem Case, the reward for Giovanni's Earth Badge.
Getting gems
Every Pokémon you defeat drops gems of its types. A Pokémon with one type drops twice as many of that type.
| Where | Gems per type | Single type |
|---|---|---|
| Route | 1 | 2 |
| Dungeon | 3 | 6 |
| Gym and trainer battles | 5 | 10 |
| Dungeon boss | 20 | 40 |
Underground plates also sell for 100 gems of their type.
Upgrades
Open them from the Bag (ITEMS → GEMS). Each upgrade adds +0.1 to one type's multiplier in one case — for example Water's super-effective hits go from ×2 to ×2.1. Each case goes up to 10 levels; level n costs 500 × n gems of that type (27,500 for all 10).
Upgrading "No effect" lets a type do a little damage where it normally does none. A type can only be upgraded in cases it really has.