There is a method you could consider, though I do not know how well it will work on a ... ghost.. egg. Find a bright light, such as a lightbulb, and put the egg next to it. One should be able to see the forming creature inside. If it looks fairly large it may be nearly ready.

[Did candling even work on ghost eggs? How did ghosts make eggs to begin with?]

A fitting name theme for spirits.

[There is a bit of beeping on Xemnas' end, as he fidgets again with this device.] If you wish a separate species, earlier I noticed one named 'Misdreavus', perhaps it would suit your requirements of cute. However I am unsure if this index lists it, or where to find it.

[More beeping. He's not bad with technology but this one's foreign.]