IVs and EVs

Polished has a hybrid game mechanics of the modern and the vanilla for stats.

IVs

The IVs in Polished range from 0 to 15 and are stored for each of the six stats. The flawless IVs would thus be FFFFFF.

• The IVs determines the type of Hidden Power as expected.
• The game has the IVs vary color option among the preferences at the start of a new game. (Oh, this seems to be forgettable. :P)

EVs

The EVs in Polished have a maximum of 252 for each of the six stats and, unlike the modern, have no limits to the total points; i.e. you can max out all the EVs of an individual Pokémon. The maxed out EVs would thus be FC FC FC FC FC FC. Each species has its EV-yield data defined as expected.

EV grinding

Polished has the Power items and, as an exclusive QoL update, lets their EV boost apply to the Exp. Share holders as well. One of the Power items and five Exp. Shares can drive you the fastest. EV grinding won't be mandatory in a regular playthrough but should be for Polished Battle Tower challenges.

Best EV training spot for each stat

• HP: Surf in the water behind the counter in Cliff Edge Gate to encounter only Wooper and Quagsire.
• Attack: Go to the Ruins of Alph, since Unown gives both Atk and Sp. Atk EVs.
• Defense: Surf in the small pond in Celadon City to encounter only Grimer and Muk. Alternatively, look for random wild encounters in Victory Road, most of whom give Defense EVs (and EXPs), while (preferably) dealing with their Sturdy with multi-hit moves or Mold Breaker.
• Special Attack: Again, the Ruins of Alph for Unown.
• Special Defense: Surf at either New Bark Town, Cherrygrove City or Olivine Port to encounter only Tentacool and Tentacruel.
• Speed: Surf at Blackthorn City to encounter only Magikarp. Alternatively, spam Old Rod or Good Rod at most towns to encounter only Magikarp and Poliwag.

Trivia

• The vanilla Gen. I and II have the IVs more determinant than do later Generations and thus let them often referred to as "determinant values" (DVs); as a matter of fact, the term "DV(s)" prevails in the code of Polished.
• The Power items + Exp. Share combo used to be a mere oversight but has become one of the Easter eggs of the game.