forget about bitcoin to buy drugs, go for pot 
being serious, there are better options now. no need to mix coins, just go for some anon coin like xmr/shadow/nav
being serious, there are better options now. no need to mix coins, just go for some anon coin like xmr/shadow/nav
Most of the dark markets accept only Bitcoin. A few of them may accept Litecoin or Ethereum. But I don't think that any of them accept these little known altcoins suhc as XMR and NAV. So it is not possible to buy anything with these coins.
You can still use those coins to go through an exchange to remove the trail of your identity.
For low amounts, you can use fake data on an exchange and still trade your xmr to bitcoin and then send the bitcoin to the dark market. Makes it incredibly hard to track you, especially if you use VPN on top of it.