I am on 408th level of excavation and I've started to get ink sacks from a dirt today.Joliver suggested me to make this post,although I'm not sure if it is a bug or some sort of a server change/update to the levels 350 to 400 maybe of excavation skill.Anyway ink sacks are not on wiki McMMO and between the rest there is said : Note: If you are bewildered on why you are getting things not on the list (ie. coal from dirt, cobble from sand etc.),please note thatit is your server owner/admin modifying the plugin and it's not original McMMO.
Getting custom items from Mcmmo abilities is something that can be altered. Whatever you obtain from excavation just assume that it was an added drop. :}
