I recieved one from a battle, but I'm afraid of feeding it to my pet. Hah! What does it do?

feeding it to your pet will make it less hungry

using it on your pet will make it slightly faster (gives your pet 1 to 3 speed stats)

Crashasaur gained: 0 level(s) 0 strength 0 defense 0 intelligence 0 health points 1 speed points

Awesome, thank you!

Using a Lightweight Egg only works if your pet is tier 1 to 3. Higher tier pets get no benefit.