What variables of an evolving Pokémon remain the same?
Solution 1:
Looks like it's just the amount of experience needed to level up to 100 and the number of egg cycles needed to hatch.
- Capture rate can change
- Gender ratio can change (most obviously, in gender-specific evolutions like Gallade and Vespiquen. But also for Azurill and Marill)
- Base happiness can change
- Egg groups can change (for baby Pokémon like Pichu)
Everything else, like types, stats, and abilities, obviously changes in many cases.