This build uses the [Rage] part of Rest & [Rage], so make sure to set your primary emissive colour to a light colour.

Most of this is a standard Mallet build. [Corrosive Projection] helps to deal with enemy armour. You want very high range so that your mallet affects as many enemies as possible. Decent duration so that your buffs last a longer time. No defensive mods because you will be relying on invisibility to stay alive. The rest goes into strength to increase your Mallet damage and the effectiveness of your buffs. As for arcanes, Energise is the important one. Combining Energise, Zenurik Energising Dash and [Octavia]'s passive will give you enough energy to maintain your ability rotations indefinitely without any efficiency mods. I used Aegis for the other arcane because it's a good general-purpose defensive arcane that can function even without any other defensive mods, but you can substitute it with anything you want.

So why use [Rage]? The main damage for Mallet comes from enemies running into Mallet range and attacking it, which means that buffing enemy speed and damage will cause them to die faster. Rage is basically a mini-Speedva effect which happens to be part of the helminth system, making it a perfect fit to combo with Mallet. The fact that you are building very high range means that the Frenzy augment fits perfectly in your build, allowing the Rage debuff to spread like pseudo-spores to speed up enemies many rooms away from you, allowing you to maintain your damage and kills.