All zombies have a small chance of having knockback resistance
Above ground
Skeletons have a small chance of wielding a wooden sword
At stone level
Skeletons can wield a stone pickaxe, a wooden sword, and a power 1 bow
Skeletons can have leather armor
Zombies can wield a stone pickaxe, stone sword, stone shovel
Zombies can have leather and gold armor
At deepslate level
Skeletons can wield an iron pickaxe, an iron sword, and a power 1 or punch 1 bow
Skeletons can have leather and chainmail armor
Zombies can wield an iron pickaxe, iron sword, iron shovel, stone pickaxe, stone sword, stone shovel
Zombies can have gold and chainmail armor
Creepers have a small chance of being fast
Spiders have a small chance of being invisible