Hi John,
The coin is one of our regular Mob of Roo dollar coins with a special mintmark (Master mintmark) - a tiny kangaroo bounding through the letter 'C'. If you check on the link in the first post above and then click on the boxed coin, a close up picture of the mintmark emerges.
During a 4 day period back in July (I think), visitors at the mint were able to use the visitor's press to get an additional C MM on the coin - these were not available to the public except to those who attended the mint in person. Apparently a few dealers were able to secure a small number of these coins, but they immediately put the price up to $30 - $35. (I think they were originally $12 to get via the visitor's press).
I did add one (Master mintmark, but without the extra mintmark) to your coin pack.