For sounding so worthless, Bottle Caps are actually one of the most valuable items in the game. They can be used to Hyper Train your Pokemon. Hyper Training will fake your Pokemon’s IVs, essentially, and alter your Pokemon’s stats so that they seem to have 31 IVs in a stat.
So how do you get them?
The methods listed below will help enable you to farm Bottle Caps. There’s no magic bullet here, it’s all about patience, patience, and more patience!
Method 1 - Fishing
Have you ever gotten an item instead of a Pokemon when fishing? Well, a Bottle Cap is one of many items that you can earn when fishing in a bubbling spot. It’s a very low chance, but if you abuse the bubbling fishing spot outside the boat in Seafolk Village, you can fish very quickly.
Enter and exit the boat to continually reset the bubbling spot. This is the most accessible, and slowest, way to farm Bottle Caps.
Method 2 - Poké Pelago and Shards
Poké Pelago has a cave where you can send your Pokémon exploring and they will bring back items. Some of them are worthless, and others, like evolutionary stones, are best farmed here. One of the routes focuses exclusively on finding colored Shards.
This is the only way to get Shards in the game and while they don’t seem to have a use, they are actively desired by an NPC in Festival Plaza. If you rack up 30 Shards of one color, he will give you a Bottle Cap in exchange.
This method can take a painfully long time because of Poké Pelago’s dependence on the days passing. The fastest you can ever get Shards is once every 12 hours (use Poke Beans to speed things up). If you choose to acquire Bottle Caps this way, you’ll want to make sure they count each time you use them.
Method 3 - Festival Plaza Abuse
First, you will need a friend who, if you ask them about facilities, will offer to sell you Treasure Hunt 2* . No, not 3*, 4*, or 5*. It has to be 2*. Buy it for 100 FC (assuming it’s your first one) and drop it somewhere.
Now, immediately go to the Treasure Hunt and play. Your first prize is guaranteed to be a Bottle Cap in this facility. After grabbing your Bottle Cap, find a friend or guest with any 1* facility that you don’t have and replace Treasure Hunt 2* with this for 50 FC. From here, install Treasure Hunt 2* again and rinse and repeat.
Getting a Bottle Cap this way costs a minimum of 100 FC, then 150 FC on subsequent attempts. But if you have some FC lying around from those huge Global Missions, this is one of the best ways to spend them.