Unpredictable Lucky Blocks
The mod «Unpredictable Lucky Blocks» introduces a lucky block that replaces one of the mobs, capable of dropping around 100 different items in MCPE. Each time you break the block, you will receive a random item (sometimes even dangerous ones). For instance, a boss wither might spawn, or you could encounter ten zombie pigmen. Fortunately, there are also beneficial drops, such as enchanted swords or similar items.
Pigs are replaced by the lucky block. This means you will find them naturally spawning in most biomes of Minecraft PE. 
Hit the block to break it. Once you do, something random will appear in MCPE. In this case, a horde of zombie pigmen emerged.
In another instance, a wither appeared!
However, it’s not always negative. Sometimes, you might receive something good, like an enchanted item.