(look at the encounter tips, the mantyll one) once you've nabbed an egg, depending on what type it is, use either torches/campfires or AC units if you're in late game. The baby will only want Wyvern milk, comfort food and normal eating, so either kill an alpha Wyvern or ko(knockout) a female, but the alphas give 8x more. Keep it in a fridge till the baby hatches -Mantyll