Gas based [Verdilac] that maintains combo to maximize gas procs for Magus Anomaly combos. CO works multiplicatively with gas procs, so does roar.
Nira's is bugged to affect all damage instead of slam damage, so go ahead and abuse that 390% damage stacked with with CO, Roar, and a Tesla proc at the end.
Switch CO for [Primed Reach] if you do not like the decay on damage, though [Reach] doesn't change too much. [Quickening] can be itself or [Primed Fury], I just like the extra combo chance.
Power Spike from the Naramon tree is essential to maintain combo, maximizing crit and status.
If you're not going a grouping or combo build you ought to take Voltaic over Volcanic that way you're corrosive instead of gas.
The Vauban build I made to go with this was not very good after the operator update - therefore this has changed to go with [Mag] on the new patch but it can go with any grouping ability that doesn't ragdoll enemies([Khora] subsume, [Mag] bubble, Magus Anomaly, etc)