Unfortunately Dash has the same fungibility problems no matter how much they try and hide it
How does it? I really want to know but nobody will tell me
Because if someone identifies outputs I own as being tainted then they can be blocked by merchants or exchanges or whatever.
"But you can just Darksend them!" is the reaction I have seen. Except that in Bitcoin you can send them to yourself and boom - new outputs. Does that make Bitcoin magically fungible? Or what if I mix the outputs using BitcoinFog, does that make Bitcoin perfectly fungible?
Fungibility is destroyed the minute you can trace transactions through the blockchain, it doesn't matter how you mix them and who is involved. Otherwise just use Bitcoin and send the funds back to yourself if they're tainted, no Dash needed!
I don't know how good BitcoinFog's mixing is, or how big their anonymity set is. But the main difference is, that it requires trust. One day when their anonymous admin runs into financial problems and looks at the Fog's wallet and sees a couple of thousand bitcoins in there, well, I wouldn't want to be mixing on that day. And you'll need to keep track of your change, basically you can't spend a change anymore until it's mixed again. And you better not send multiple changes in one transaction to the Fog as it will tie the two changes and hence the two transactions you made together. It's very easy to do a mistake like that. DRK/DASH wallet on the other hand will take care of this.