This script is for Pokémon Essentials. It displays egg sprite based on pokémon first egg group.
Doesn't work on Essentials versions 18.1 and older. To see other Essentials versions, look at all branches.
Follow FL's Essentials plugin installation instructions.
If the species was an egg graphic (like Manaphy), the graphic still will be displayed. Species that can't breed like Igglybuff uses it's evolution species egg group.