In each level in Super Mario 3D World, you can easily progress through each level and find the flagpole. However, if you want to 100% complete the game, you need to find all three green stars and the stamp hidden throughout each course. Some of these are easier to find than others. Sometimes, you can play through a level multiple times and have no idea what you are missing. The World 5-4 stamp is one of those cases. Here is where to find the stamp in Sprawling Savanna.
While it is easy to pass this collectible and have no idea it was even there, getting to the stamp itself is incredibly simple. Load up the level and progress until you are shot out of a cannon to a wide-open field.
There is a bunny you can chase down for a green star in this area, but for what we are looking for, you need to go to the other end of the field. There will be a line of Ant Troopers coming out of a wall and going into a hole in the ground. Jump down that hole.
Inside that hole is a giant Ant Trooper walking around the cubical room with the stamp you are looking for attached to the backend of it.