The older games in the Pokémon series made it difficult to detect the Individual Values of Pokémon stats, but it's possible to easily check them in Pokémon Sword & Shield in the post-game, so long as the player is able to crush Leon in a second battle.
Individual Values (better known as IV values) determine how much a Pokémon's stats will increase when it levels up. A Pokémon's IVs are determined when it's created by the game and encountered by the player for the first time, but the player cannot easily find out what they are without outside help. It's possible to unlock an IV Checker in Pokémon Sword & Shield that will judge a Pokémon's stats based on their IVs while they are in a Pokémon Box, but the player needs to work for it first.
Defeat Leon & Capture The Box Legendary
The first stage is simple enough. The player needs to complete the main story of Pokémon Sword & Shield, which involves the battle against Eternatus/Chairman Rose and completing the Champion Cup. The last opponent is Leon - the Champion of the Galar region. Leon will use a team of Level 60+ Pokémon with a line-up that is different depending on the starter Pokémon chosen by the player at the start of the game. The team will always contain an Aegislash, a Dragapult, a Haxorus, and a Charizard that can use the Gigantamax transformation.
Once Leon is defeated, the player can then finish the post-game campaign. This is started by going to the Slumbering Weald and it culminates in a battle against the box Legendary (Zacian for Pokémon Sword or Zamazenta for Pokémon Shield) and one last battle against Hop.
Go To The Battle Tower
Once Hop is defeated, the player can return to Wyndon and visit the Battle Tower. The rules of the Battle Tower are simple - no Pokémon are banned (including Legendary/Mythical Pokémon) but the player cannot use two Pokémon of the same species and all held-items on the team must be different, so no multiple Leftovers. Flat rules apply, which means that Pokémon above Level 50 will have their levels lowered to 50. The player can choose between Single Battles (with a team of three Pokémon) and Double Battles (with a team of four Pokémon).
As the player wins more battles, their rank will increase. The ranks are Beginner Tier, Poké Ball Tier, Great Ball Tier, Ultra Ball Tier, and Master Ball Tier. The opponents get stronger as the player's rank increases.
Achieve Six Victories (Including A Rematch With Leon)
In order to unlock the IV Checker, the player needs to win six battles in the Battle Tower to increase their rank to Poké Ball. The sixth battle will involve a rematch with Leon, whose team will be level 50, but the line-up will be chosen randomly from a list (with the exception of Gigantamax Charizard). Defeating Leon will bring the player up to rank 4, which will unlock the IV Checker.
To use the IV Checker, the player needs to put the Pokémon in a Pokémon Box and press the plus button. This will list the Pokémon's six stats and a statement next to it will give the player an impression of the IVs. If it says No Good, then the stat has no IVs, if it says Decent, it has 1-15, if it says Pretty Good, it has 16-25, if it says Very Good, it will have 26-29, if it says Fantastic, it has 30, and if it says Best, it will have 31.
Pokémon Sword & Shield are available now for Nintendo Switch.