This is the build I use mainly for the [Nekros] farming and other tanks in long lasting mission.

With the umbral mods you should abuse heavy attacks as a mean of crowd control and target priorization, thus using the full mod's potential.

If you are poor, you can replace [Blood Rush] and [Condition Overload] with [Quickening] and [Fury] (that was my previous build) and still manage to deal decent damage. If you plan to do that, then you just need 2 forma if you also replace [Shocking Touch] with [Voltaic Strike] (for a total of 3 Madurai V polarities). This will decrease dps by ~20k.