I saw once, maybe on this site, people making eggs that looked like the pokemon they contained. Am I allowed to ask how people would do this, because i would really want to learn how to do this?

It's just a normal sprite fusion, I'm pretty sure. You can see a lot of them on Pokefarm. I've took some sprites of Pokemon and eggs and snapped parts on the eggs... I think that's what it is.

I have very little idea of what you just said. Could you explain in detail please?

Here's a template: Just add the colors/patterns from the pokemon's sprite and that's it.
Keep in mind the darker area on the bottom and the lighter one on top.

what program did you use?

ms paint but I cheated with the ovals, I needed them bigger so I expanded them and pasted them back in paint

How did you do it? Free hand or pasting the shapes?

free-hand, just using the pokemon's colors to recolor the egg

Ok, this is probably getting frustrating for you, but could you just clarify.

You go onto paint, paste a picture of the blank egg, draw an outstanding feature of the pokemon onto it, eyedropper the colour of the pokemon you are egging, and thats it?

more or less ya that pretty much sums it up, i made a few of different eevee evolutions myself just doing that (yes i know you have to evolve eevee to get anything else and you cant just hatch and umbreon strait from the egg but w/e, there isnt a real mew fused with a dragonite either)