In Pokémon Emerald, several more mechanics were added. A Pokémon's nature could be influenced if its mother held an Everstone while in the Day Care, while Pokémon with Magma Armor or Flame Body shorten the hatching process if they are in the party with Eggs.
Pokemon that can have flame body: Magmar, Slugma, Magcargo, Magby, LItwick, Lampent, Chandelure, Larvesta, Volcarona, Fletchinder, Talonflame
Pokemon that can have magma armor: Slugma, Magcargo, Camerupt
Pokemon whose hidden ability is flame body: Ponyta, Rapidash, Moltres, Heatran