From the Super Mario Wiki, the Mario encyclopedia
A jack-in-the-box is a kind of toy found in Shy Guy's Toy Box in Paper Mario. When Mario Ground Pounds one or Hammers its box lid while standing on top of it, the lid flies up, making Mario jump very high. When the box opens, a fake clown sticking his tongue out would appear. The box then closes, hiding the clown. Jack-in-the-boxes are very similar to Trampolines.
They return in Mario Party 5 on the board Toy Dream. If one lands on a Happening Space on a present, it launches the player to another part of the board. In this game they have a Koopa Clown Car-like face.