Ruby and Sapphire breeding, EVs, IVs and natures
Use the Route 117 Day Care and original Generation III inheritance and training rules.
Original Pokémon Ruby Version and Pokémon Sapphire Version for Game Boy Advance. Version-specific encounters and story roles are labelled. Emerald and the Nintendo 3DS remakes have separate rules and progression.
Find a compatible pair
The Day Care on Route 117 accepts two Pokémon. Compatible opposite-sex parents normally share an Egg Group; the offspring generally belongs to the female’s basic evolutionary family. Babies and the Undiscovered group do not produce Eggs. Ditto can pair with many species, but Ruby/Sapphire provide no normal wild Ditto location, so a Ditto breeding plan needs a compatible trade.
Use the original inheritance rules
Up to three distinct IV stats are inherited from the two parents; the original selection code can repeat a stat, leaving fewer inherited values. Ruby/Sapphire do not use Everstone to inherit a nature. Egg moves can pass from the father, eligible TMs/HMs can also pass from the father and a compatible level-up move can be inherited when both parents know it. Check the species profile’s Egg moves before arranging a pair. Azurill requires Sea Incense and Wynaut requires Lax Incense on a parent; otherwise the Egg is Marill or Wobbuffet.
Hatching needs steps
Collect an Egg from the Day Care Man when it is ready, keep it in the party and walk or cycle until it hatches. The species determines its base Egg cycles. Flame Body and Magma Armor do not accelerate hatching in original Ruby/Sapphire; that party benefit arrives in Emerald. Day Care levelling can replace old moves, so inspect parents before taking them back.
Train EVs separately from IVs
EVs are earned from defeated Pokémon and affect stats; the limit is 510 total and 255 per stat in these games. Values divisible by four avoid wasting the final points in a level-100 plan. Vitamins add EVs only below their original per-stat limit. Macho Brace doubles earned EVs while lowering battle Speed, and Pokérus doubles earned EVs. The friendship Berries do not remove EVs in Ruby/Sapphire; that effect begins in Emerald.
Keep a practical training record
Record the intended nature, key IV stats, four moves and EV targets before investing rare items. A story team does not require perfect values. For the Tower, check the room’s level and make sure a planned level-up move will be available without exceeding the Level 50 entry limit.
Use the Ruby or Sapphire version listed in the record. These guides cover the original Game Boy Advance games.