TL;DR: For NTSC-U/C, as of November 2024, a Clefable with Soft-Boiled in SwSh is most cheaply obtained at $447.99 USD before taxes. You will need LeafGreen, Diamond/Pearl, Black/White, Shield, a DS Lite, a 2DS, HOME Premium, and a Switch Lite.
Soft-Boiled is only obtainable on Clefable via Generation III Move Tutor. This means the following games are necessary to transfer a Generation III Clefable into Sword and Shield.
- A Generation III game
- A Generation IV game
- A Generation V game
- Poke Transporter
- Pokemon Bank
- Pokemon HOME
- Sword or Shield
Here are the steps:
- Catch a Clefairy in FireRed or LeafGreen
- Evolve Clefairy and teach it Softboiled in Celadon City
- Transfer Clefable via Pal Park to a Generation IV game
- Transfer Clefable via Poke Transfer to a Generation V game
- Use Poke Transporter to move Clefable into Pokemon Bank
- Connect Pokemon Bank to Pokemon HOME and transfer Clefable
- Move Clefable to Sword or Shield
The following non-cartridge hardware is necessary to perform these steps:
- An original DS or DS Lite (for dual-slot mode; allows you to play FRLG, transfer into a Gen IV game, and transfer into a Gen V game)
- A 3DS with Poke Transporter and Pokemon Bank pre-installed (serves as the middleman between Gen V and HOME)
- A Nintendo Switch (for HOME and SwSh)
I have listed the cheapest possible option, in USD, for each necessity. These are generally accurate as of November 2024 and assume you're playing on NTSC-U/C products.
- Pokemon LeafGreen ($95)
- Pokemon Diamond or Pearl ($40)
- Pokemon Black or White ($70)
- Pokemon Shield ($30)
- DS Lite ($30)
- 2DS ($80)
- Pokemon HOME Premium ($2.99 monthly or $15.99 yearly)
- Switch Lite ($100)
Note that your 3DS must already have Poke Transporter and Pokemon Bank pre-installed, as the closure of the 3DS eShop means they can no longer be downloaded (legally, that is). Pokemon Bank has no subscription fee anymore.
This works out to $447.99 USD with the monthly HOME pass, or $460.99 with the yearly pass. Be sure to perform due diligence when purchasing products; many cartridges floating around are fake and only serve to waste your money. If you're wondering where to get $447.99, a helpful guide can be found here.