Basically anything can be stacked.
Var and NPP make a nice stack. BUT, make sure you have done a cycle of both SEPARATELY first, to judge your reactions to the compounds. Doing them separate first can help you dose properly and evaluate sides as well as results. Doing them together might not be as beneficial as you think. More is not better.
Also, stacking is better for the more advanced AAS users. You need to be VERY aware of what sides to expect (and how to notice them in their early stages), and how your body reacts to compounds. Knowing your tolerance is critical.
What is your history with AAS, more specifically, these 2 compounds? Goals?