So here's Mav's unique stats and gear:
3+ / 4+
Pistolier: Maverick has mastered his own duel pistol combat form. He can fire both weapons each shooting phase, and as they are both assault weapons can assault the same turn and gains +1 Attack for wielding two weapons.
Gear: Power armor, K & F grenades, iron halo, plasma pistol, Nova Pistol
Nova Pistol: The Nova Pistol is a relic of the Crimson Fists trusted to Captain Maverick alone. The chapter techmarines act as custodians for the weapon, who study it in hopes of rediscovering ancient advances in plasma technology; the Nova fires in two different modes and is not prone to over-heating as other plasma weapons are. In close combat its bolts burn through even the toughest armor (counts as a power weapon).
In the shooting phase Maverick can fire in one or two modes:
-- bolt [R12” S6 AP4, assault 1]
-- blast [R12” S3 AP6, assault 1, blast]
* * *
So is it legal? Yes, it is. The big secret behind the Nova pistol is one simple 15 point option: the Auxillary Grenade Launcher. The AGL can be fired in addition to another shooting weapon, fires frag or krak grenades, and is assault 1. For another 15 points I bought him a power weapon, which combined with his plasma pistol (another 15 points) gives him Attacks +1 which ignore armor.
Is he effective? Well, I think I've actually only used him once, against Known as Ben's dark eldar and I don't think he got to fire a single shot! His command squad was assaulted by incubi or wyches and were tied up until eventual death. But I still like him.