DRASTIC improvements to Pokémon movepools. Dark-type is now Physical while Ghost is Special. Fossils + GS Ball added to Ruins of Alph.
Gen 2 trade items now simply work like evolution stones. Kanto locked Gen 2 mons like Houndour added to Johto. Players who don’t grind will still be under leveled to the champion, but this is intentional and typical for most Pokémon games. The game now sees a more linear rise in leveling, with expanding trainer teams to provide more EXP. Gym leaders and trainers no longer fall off in the late mid-game, only to spike in the Elite Fuur. Movepools see increasing diversity and complexity. Bugsy keeps his Scyther, but Metapod and Kakuna are replaced with Pineco and Ledian).
Leaders see more Gen 2 representation, while still retaining their original aces (e.g. The team’s and levels of Chuck, Pryce and Jasmine scale to whether you have 5, 6, or 7 badges. This ensures an authentic gen 2 experience, while bringing the game to it’s full potential. Rather than bring modern Pokémon design philosophy to Crystal, Legacy only makes changes based off precedents set in the game’s original design.
Pokémon Crystal Legacy is an enhancement hack that aims to improve Generation 2’s most underdeveloped areas, whiling holding on to the mechanics and feel that made it unique.