Except for the Trelk, which i'll explain later on, Mirg has no national currency, whatsoever.  (That is unless you consider Shash to be currency, which more than a few people actually do.)

The reason why Mirg has no national currency is because its government is conscious of itself.  Goblins know that, in general, the other races of Telgard think of their race as a bunch of untrustworthy backstabbers.  And, for the most part, Gobs admit to it.  If done correctly, backstabbing is GREAT for business, it is a highly effective and useful skill.  So instead of creating a Goblin currency, which would take far too much energy trying to convince the other races that it was actually valuable, Mirg just uses the money created by the other Kingdoms. 

Since gobs very frequently travel into foreign kingdoms and trade with the inhabitants of those Kingdoms, Mirg is absolutly full of foreign currency.  Gob Merchants are also very in touch with what is going on in the foreign markets, so the value of a certain coin from a foreign country is worth almost exactly the same in Mirg as it is in its native kingdom.

A Trelk is a type of banknote given out from the only bank that has ever existed in Mirg.  It was established in Krull only 30 years ago, by a very young and very rich gob named Trelk.  :)    Currently trelk is only in circulation within the Fortress of Krull and is used very rarely by anyone but the extremely poor.  To most Gobs, using a bank to keep your money is thought to be outrageous.  A cookie jar or a bed mattress tends to be a more preferable place to put ones money, than in a bank.

However it has now been 30 years since Trelk had opened his bank, and started handing out paper trelks as loans to the absolutly desperate, and the value of the trelk has begun to rise a bit.  The value of the Trelk compared to Korreshian currancy is 1.5 greater than the Sorrchep or Zinc coin.