King's Coins
King's Coins are actually chocolate coins covered in gold leaf. They were the last great creation of Wally Wanka who made them especially for the King. They were so good and so prized, that people actually use them for currency.
King's Coins are special items. They have the same teal labels as quest items. They are Soulbound immediately when received and hence cannot be traded or sold. They are offered as rewards for certain Quests, and can sometimes be dropped as loot from monsters and chests. They can also be obtained by completing a Relic Quest, where they will be found in Ancient Relic Chests, sometimes after defeating the Chest Guardian. Some people will farm repeatable quests, to collect King's Coins. They can be spent at the Token Masters or at Sam's Dungeon Wholesale. Token masters give yellow or rarely purple items for them while Sam will give purple items or very rarely rainbow items. The cost of items is dependent on what category the item is in and whom you purchase it from. Sam's costs are higher than the Token Masters due to him giving better items.Another important function of King's Coins is that they can be tossed into the Wishing Well.
Presently, it is possible to have up to 100 King's Coins in one stack. Previously (before Chunk 2), they stacked up to 10, but if you got them as a reward for an amazing relic, then you received a stack of 20!
A rare version of Gypsy Sally sells King's Coins for a high price. Some high level characers who have completed all the quests buy these KCs to spend with Rainbow Sam.
Now there has been many a fight over who should get your Coin and when. The best solution depends on the amount of Coin you have. Usually though they should go to the Token Masters in town. They may only give yellow equipment but if your equipment is way out of date and you can't keep up with the monsters anymore it may be a good time to use them. The occasional expenditure on Mythic(Rainbow) or Unique(Purple) Sam is worth it sometimes. Use them to early and you may find yourself unable to get the current equipment you need. Use them to late and you will save up coins you will never need. And of course the other option is to throw them in the Wishing Well!