I want to make a mug cake, can I use hot chocolate mix instead of cocoa?
You definitely want to use cocoa powder if you can...but...

I've done it in a pinch. It's not as good as cocoa powder though because hot chocolate mix is usually also sugar &amp; sometimes powdered milk. But it's still something to fix a chocolate craving when you don't have much else in the cupboard. 

I've added hot chocolate mix to waffle mix/pancake mix and always found it delicious, though of course not as chocolate-y as with pure cocoa powder.