"Pokémon: Let's Go" Hyper Training Guide and Bottle Cap Farming
Hyper Training and Individual Values
If you've already beaten the Elite Four and have unlocked all the end game features, Hyper Training is something you might be interested in. If you don't know about Pokémon Individual Values, they're hidden stats that are unique to each individual Pokémon that give them a boost to each major stat category. The randomize per stat and generally, you want the highest possible boost per stat. For more details feel free to check out my guide on Judge and IVs.
Hyper Training is an end game feature that lets you max out your Pokémon's individual values. This is the only way to modify a Pokémon's individual values, without it you're stuck with trying to find a new Pokémon with better IVs. If you're interested in doing that, feel free to check out my guide on catch combos and shiny Pokémon as catch combos are the best way to catch a high IV Pokémon.
Hyper Training requires your Pokémon to be level 100, and also requires a Bottle Cap or Golden Bottle Cap.
Visiting Mr. Hyper
In order to actually Hyper Train your Pokémon, you need to visit Mr. Hyper. After beating the Elite Four, you can find Mr. Hyper in the Pokémon Day Care just south of Cerulean City. You'll have to cut down the brush on the southern side of the city but otherwise, it's a very short walk (Alternatively you could just fly). He's the old man standing next to the counter, you won't miss it.
Hyper Training a Pokémon
When you speak to Mr. Hyper, he will allow you to hyper train in exchange for Bottle Caps. You'll select a Pokémon, a stat or all stats, and then he'll train them. There isn't much of a sequence, just Mr. Hyper making some noises, and then without any really good visual reinforcement, your Pokémon's selected IVs will be maxed! There's no limitation on how often or how many times you can do this.
Obtaining Bottle Caps
Bottle Caps are quite difficult to come by, but there are some reliable sources.
To get regular Bottles Caps, you'll have to battle Mina. Mina is a Fairy Pokémon trainer that you can find in Vermillion City. You may have fought her back when you first visited the city. After beating the game, you can battle her repeatedly, once per day. Each time you defeat her, she'll give you a Bottle Cap.
To find her, you'll have to navigate down to the docks, close to where you first got on the S.S. Anne. She's a fairly easy fight with only 3 Pokémon in her lineup with levels in the 50s. For what it's worth, Poison and Steel counter Fairy, but I doubt you'll struggle with her given the Elite Four are likely more challenging.
Obtaining Golden Bottle Caps
Golden Bottle Caps are a lot more difficult to come by than regular Bottle Caps. Given these items will max out ALL of the IVs of your selected Pokémon, it makes sense they're so difficult to find. Unlike regular Bottle Caps, there is no guaranteed source of Golden Bottle Caps. However, similar to the battle with Mina, there is a daily repeatable way to attempt to get one.
There are six hidden items in the Celadon Game Corner. Each hidden item could be any number of things, but they could be a Golden Bottle Cap. These hidden items refresh daily. A time-consuming but clever option to ensure you get a Golden Bottle Cap is to save your game right before picking up all the items. In the event you don't find a Golden Bottle Cap, you can go back to your Switch's home, close the game, re-open it, and restart your save and try again. Items are randomized upon picking them up, so you can keep doing this until you get a Golden Bottle Cap. Then, do it again the next day to once again ensure you find one. This is very time-consuming as Golden Bottle Caps are quite rare, but it's still probably the best and shortest way to max out your Pokémon's IVs so you can make that decision yourself.
Refer to the images below for the locations of the six hidden items.
Celadon Game Corner Hidden ItemsClick thumbnail to view full-size
Bottle Cap farming, maxing Pokémon IVs, and even getting Pokémon to level 100 is really only a goal for the most intense of trainers. It's not necessary for the regular game in any way, shape, or form. However, for those who want to battle other trainers in real life or just generally want to be the best there ever was, there is a ton of value in these systems. If that's what you're into, good luck with the farming!