Very valid points. I would love to have the eggs hatch inside as well. But that will be more tricky to look nice. An egg is a nice simple shape to push out, some kind of monster (maybe goblin) will be more complicated
Doesn't need to be a monster, when it thematically wouldn't make sense.
How about you have a groper tentacle (style thing) slowly emerge from the hole, and then disappear below. So it would then need a backend as well, but you'd then be reusing an existing mesh/texture, just used in a different manner. Maybe a little smaller or several escaping at once.