This guide will provide you the location where you can find the suspicious egg.
You have to start by entering into the huge castle. You will find a board with some text written on it, so you will need to be careful as this is a suspicious place.
Enter the castle, climb up the stairs on the left side and move into the room.
After that, exit this room from the left side and move down the stairs. You will enter another room where you find the suspicious egg.
There will be a conversation between you and Sussus Amogus. Ask him that you want that suspiciopus egg. He will agree to give you. Pick it up and go to your inventory but you will not find the egg in the inventory.
Then he will ask you to go to the top of the castle in order to get the egg. Exit the room and make your way to the top and you will find that you have been april fooled by him.