Supernova question

[Vinsdor]

Got my first unique fire missile.It says it can cast supernova: synergy with lightning.How does it work?Should I aply lightning control or mastery before this?

[Space_Void]

Pretty much but is fkin annoying to switch styles in the middle of a fight.

[Xenos]

I believe synergy relies on you having hit the target with at least one of the two sigils, but requires you to deal overkill damage to charge the synergy bar. I'd probably recommend mastery.

[Eden]

There's a full explanation here: http://steamcommunity.com/sharedfiles/filedetails/?id=289981046

The short version is: craft the unique shape into a spell with the primary Sigil (in your case Fire). Then make sure you have that spell equipped as well as the secondary Sigil specified in the unique (in your case Lightning). If you do that the Synergy is considered active and you will see a little gauge in the primary Sigil spell UI (the thing in the bottom righthand corner).

You then need to tag mobs with either Fire or Lightning spells (any effect will do, DE CO or MA) and kill them. Any overkill damage goes towards charging the synergy (the tooltip will tell you how much overkill damage you need. You get a bonus if you tag a mob with both Sigils' effects (i.e. Fire and Lightning). Once the synergy is charged it occupies the AoE slot of the primary Sigil (i.e. Fire). Enjoy!

And yes, MA -> DE or MA -> CO -> DE is a great way to deal overkill damage.