In this mod, there is a 5% chance of a mob dropping a crate when you kill it, and a 1% chance of it dropping a key. There are currently 20+ series of crates within the mod, and each has a unique combination of random loot. Additionally, there are 16 paints that can be used as an infinite source of dye! You can currently dye white wool, hardened clay, glass, and glass panes. Next there is the strangifier. Just combine this with the item of your choice in an anvil and every mob kill you get with that item will add to it?s kill count! Then there is the unusual effects. You have a 2% chance of getting a random unusual effect when you open a crate. Finally there is the scrap system. You can combine an iron ingot and a gold ingot in an anvil to get 1 scrap. If you combine 2 scrap you get 1 reclaimed, and if you combine 2 reclaimed you get 1 refined. In a crafting table, 2 refined will get you a key and 3 reclaimed will get you a strangifier. You can then smelt the refined to get 2 reclaimed, and smelt the reclaimed to get 2 scrap.
There is a configuration file you can use to edit the chances and other stuff.