A Digging Zombie is a baby zombie in vanilla minecraft which has +0.25 speed on his carapace. In essence somewhere over speed VI... (the "chestplate" the digging zombie wears)
A Golden Pickaxe that can easily break through grey stone and somewhat fast through blue stone. The pick does +15 attack damage and has a low amount of durability. If the Pickaxe breaks, the Digging Zombie has very little purpose as far as attacking dwarves goes.
The Digging Zombie gets Strength at night and in the dark, similar to the Fury of The Night upgrade for regular Zombies.
When Digging Zombies spawn, BruceWillakers will say this message: