1. 4 Dispensers 2. 1 Button 3. 16 Cobblestone 4. 1 Fence 5. 1 Wooden Pressure Plate 6. A few Stacks of Spawn Eggs
1. Make a one block high tower to the height you want the spawner. 2. Place 4 blocks in a “diamond” pattern. In the center place a fence. 3. On the fence, place the pressure plate. 4. Take the dispensers and place them on top of the diamond shaped blocks, making sure they are facing towards eachother.
5. Place Cobble on top of the diamond shape. 6. Place a button on one of the pieces of Cobble either above or below a dispenser. 7. Fill the dispensers with Spawn eggs of your choice. 8. Press the button, and the mobs will come flying out!
When the button is pressed, a single mob is spawned, but as it hits the pressure plate, it spawns more from the other dispensers. Once the mobs fall out through the fence, the pressure plate will reset, causing the dispensers to shoot out 4 more mobs.