ALL RUBY & SAPPHIRE EVOLUTIONS
Hoenn introduced beauty-based evolution for Feebas and personality-value-based evolution for Wurmple's split into Silcoon or Cascoon. 135 new species brought fresh three-stage chains and branching paths. Trade evolutions now include held item requirements for Pokemon like Huntail and Gorebyss.
HOW TO EVOLVE POKEMON
Max out Feebas's Beauty condition by feeding it Pokeblocks made from dry-flavored berries, then level it up. The catch: Feebas itself is absurdly rare, appearing on only 6 random tiles on Route 119 that change daily. Finding one is harder than evolving it. Use a Super Rod and be patient.
Wurmple evolves into either Silcoon or Cascoon at level 7, and which one you get depends on a hidden personality value calculated when the Wurmple is caught or hatched. It's not random each time it levels up; it's predetermined. There's no way to control it in-game. Silcoon becomes Beautifly, Cascoon becomes Dustox.
Beauty-based evolution (Feebas), personality-value branching (Wurmple), and specific held item trades (DeepSeaTooth for Huntail, DeepSeaScale for Gorebyss via Clamperl). Gen 3 also introduced abilities, which don't directly trigger evolution but changed how Pokemon function pre-evolution. The contest-stat evolution method for Feebas was unique to this generation.
Not all of them. Ruby and Sapphire famously can't connect to Gen 1/2 games. The internal dex has some older Pokemon as catchable, but others are missing entirely. You can evolve any Gen 1/2 Pokemon that's in the Hoenn dex, but Pokemon not coded into the game can't be obtained at all until FireRed/LeafGreen came out.
The Abandoned Ship has a hidden Water Stone and Thunder Stone. The Fiery Path has a Fire Stone. Leaf Stones come from various hidden item spots. You can also get random stones from the Pickup ability, so having a Zigzagoon with Pickup in your party while grinding is a solid passive farming method.