Very low apparently xD It would be cool to add triple drops if there are more ways to increase the double coin chances in the future and the chance overflows past 100%, but it is something of a very low priority to add right now. The closest I can think of right now is a special monster that spawns at a low chance and it drops multiple coins.
Treasures for the low tier monster became useless after access of lich and after. Maybe add % on the monsters' skill based on the no./quailty of treasure
 "Arcalona"){kind=icon}
 "Sort the Court!"){kind=icon}
 "Coralcraft"){kind=icon}
 "Small Dungeon"){kind=icon}
 "Enchanted Heroes"){kind=icon}
 "Alchemy Idle Clicker"){kind=icon}
 "Coloruid 2"){kind=icon}
 "Deterministic Dungeon"){kind=icon}
 "S.T.A.N.D."){kind=icon}
 "Auction House Game"){kind=icon}
 "Square Panic!"){kind=icon}
 "Heavy Weapons Guide"){kind=icon}
 "Cave Heroes"){kind=icon}
 "Zombidle"){kind=icon}
 "Accelerator"){kind=icon}
I'm considering doing a content update in a while which would include some new ingredients as well as unique combinations.