In order to build the Maneki Neko - basically a Monkey Bomb but used in the main easter egg - you'll need to find three parts scattered around the map. Each of these parts have three different locations it can randomly span to each game.

Maneki-neko

Furin

Karakuri

Once you have all three head on over to the Workshop and use the crafting table that is there. You'll get your first one for FREE but each one after that will cost 500 salvage.