From the Super Mario Wiki
The Pinball Block is an object in Wario Land 4 that only appears in the Pinball Zone level. It is a block that guards the door to the next room. It has a digital face that counts down how many Pinball Slots remain in the room. Wario must throw a Pinball in each of the four Pinball Slots. They have a mouth which opens and closes on regular intervals, determining whether or not the Pinball will enter the slot. If a Pinball is correctly placed in a Pinball Slot, the slot will disappear and it will drop a Bronze Coin. With every Pinball Slot filled, the digital number on the Pinball Block will decrease by one, beginning from four. When it reaches zero, it will flash briefly and disappear, dropping a 500 Coin and granting access to the door, which will lead to the next room in the Pinball Zone. There are a total of six Pinball Blocks amongst thirteen individual rooms in the level.