Hatching 3 (Nesting Egg enters the battlefield with three Shell counter(s) on it. At the beginning of your upkeep, remove a Shell counter. When the last one is removed, sacrifice Nesting Egg.)
When Nesting Egg hatches, create a colorless Nesting Egg artifact token with Hatching 2 and "When this card hatches, create a colorless Nesting Egg artifact token with Hatching 1 and "When this card hatches, create a 10/10 colorless Egg Titan creature token with indestructible.""
this reminds me of Reef Worm and pals. Wonderful design space