Confused About The 2 Dollar 1999 Nunuvut Coin

how many of this coin are there?
i see a normal 2 dollar one made of nickel, a 2 dollar with a gold plated interior, a 2 dollar with a solid gold interior, and a mule that looks like the plated or solid interior coin.
how many different varieties are there and how can I tell which is which?
I know how to tell a normal 2$ from a mule with the lack of a raised ring, but how to differentiate between a mule and the gold ones (without having it in hand)?.