The Mysteries of Pokemon Eggs - Flash Comic

It's weird how Pokemon like Eevee and Pikachu can lay eggs cause they're mammals. . Unless they're all Echidnas(an egg laying mammal) or a platypus. .
Also, how can Pokemon like Voltorb and Magnemite lay/make eggs or reproduce?
Skitty and Wailord, the two Pokemon that can breed somehow....despite their size difference...