In addition to the usual knife Kerr-Nau brings a breaker pistol, D-Charges, and Plasma Rife with Pitcher. Kerr-Nau also has an EI Killer Hacking Device with access to the Maestro program making him deadly against all kinds of hackers. If that wasn't enough, his device has White Noise allowing him to hide from or assault visor troopers with great effectiveness.
ARM 1 and BTS 3 give Kerr-Nau basic defense against fire and hacking. He also has the rare Bio-immunity allowing him to save against Shock and Viral with his BTS. This has the side effect of making him better against a mine hit than his stats would suggest. Kerr-Nau has Hyperdynamics like most Nexus making him an effective dodger. Last of all, Kerr-Nau can use hacking programs Cyber Mask to hide as an Impersonation 2 token or White Noise to avoid being seen by Visor troops.
Use White Noise to get the drop on any enemy with a Visor. Alternately, you can drop a pitcher and let a companion use it to move or attack MSV units unawares. Kerr-Nau is not the greatest hacker, but combined with Bit and Kiss or one of the EI's many other solid hacking choices, he can put repeaters up and greatly increase the effectiveness of other models.
In Onyx, Kerr-Nau can be part of a unidron fireteam and move up board to get into a good position before using Cybermask to move past mines and enemy LoF and put his plasma rifle to use.
Kerr-nau's plasma rifle is very frightening in Suppression Fire, and he can also enter Impersonation state and end in a good ARO position against a link team to force them to remove you or take multiple casualties from your template weapon.
Never forget that he has D-charges and can accomplish the Sabotage classified objective.
Kerr-Nau brings a lot of utility to the board but is fairly easy to kill even in hacking. Be careful if he is in a Unidron link, as this may grant him Sixth Sense Level 2, better BS, or Tin-bot against hacking. It is worth removing at least one of the Unidron's before shooting at him, because his Plasma Rifle is a very deadly weapon. Generally though, Kerr-Nau will die to most high quality shooters.
Kerr-nau is a good inclusion in almost any list. His unique contribution of White Noise and one of two Pitchers offers great tools to support other Combined units or be useful on his own.
In Onyx, should you be running a Unidron Link, it is absolutely worth bringing him either as part of the link, or a 6th man to add into the link after it has been damaged. He can also work well as part of a back up link, for example bringing a Rodok core and two unidron plus Kerr-Nau as a backup should the Rodoks be destroyed.
Kerr-Nau wants to be as far from enemy fire as he can, but do keep in mind his hacking area. If White Noise would be useful for any of your troopers be sure he is deployed with his hacking area fully within the place you would need it. You can also place him within a short move of a good LoF to a Pitcher location.
In either case keeping him safe is key.
Active Turn Role
Kerr-Nau will be working with a link or on his own to accomplish objectives. He is a support piece and in the active turn will look to buff other units, remove hackers, expand your hackable area, or make use of his Plasma Rifle when he has a good shot. Kerr-Nau will often spend time moving up the board in a link team or as part of a Coordinated order until he can get into a good position either for fire or hacking. He is not by himself a powerful piece but can improve other models, be improved himself by a link, or accomplish key classifieds or piece removal. You are paying for a lot of utility with this profile, so be sure you are getting use out of it.
Kerr-Nau has Hyperdynamics meaning he will often find himself better off dodging than shooting, however, if you can catch multiple enemies in a single template it might be worth risking a shot instead. In a link he is likewise usually better shooting and most enemies will be careful not to give him a chance to make use of his Plasma Rifle. Kerr-nau can kill enemy hackers in ARO but is not as good as comparable options in other forces. However Bio-immunity does grant him some defense against the deadlier hacking programs and means he can be treated by a medic and get back in the game.