Ermine's Tail:[1] has a variable drop rate. The drop rate depends on how many mods you add onto your maze to make it tougher or weaker. The exact drop rate is not known, i can give you my personal experience that i am 0/10 but thats with 2 different set ups. 0/3 with a Harder version (higher supposed drop rate) and 0/7 with an easier version (Low low drop rate)