Done it - or something like it, anyway. The 'extra' was a Sororitas Palatine, who'd been assigned as a representative by the Ordo Hereticus after [Classified Shenanigans] for a few missions and just kind of hung around afterwards.
The Palatine is a good place to start for a militant inquisitor because she can be reasonably close in capability - yes, she doesn't get an Angelus-calibre bolter, but hers is best craftsmanship, so it doesn't jam, and when gunning down generic goons in a horde the diference is minimal. She gets powered plate and can get unnatural toughness x2 from a relic.
I know Lynata's not a massive fan of the acts of faith (and I agree) but you can build her as the 'grizzled veteran' type quite easily instead of the tactical miracle dispenser - talented (command) and a good fellowship plus not being an 8' genebulked killing machine makes her a very good commander for requisitioned troops, or there's an ability which gives her hatred (everything), extra bonuses for things she actually hates, and proven (3) against any hated target.
Essentially, the Ascension book for Dark Heresy is your first port of call. I'd also get Heed The Higher Call for some quick pre-generated ascension characters for more rapid character generation. Note that just because the character is an inquisitor or interrogator, they needn't necessarily take those archetypes - a militant inquisitor could easily use the Judge, Palatine, Stormtrooper or Desperado archetype for his rules.
XP is 13,000, same as for a Deathwatch marine. As noted, keep an eye on how rules work in crossover. I strongly recommend avoiding psykers, as DH uses different rules for psychic powers, and the Primaris Psyker is one of the archetypes often pointed at as being overpowered. (The other being the Vindicere Assassin).
How does it affect the game?
- The Inquisitor doesn't benefit from or provide cohesion. So you've got a lower pool to work from and he can't benefit from squad mode abilities.
- The inquisitor doesn't get requisition. The equipment listed as starting gear for the class can be considered standard issue weaponry. Allow pretty free reight to tailor, though. Anything 'normal' should be available at best-craftsmanship, and rare and exotic stuff should be an option instead too.
- The inquisitor does get an Influence score. Checking influence can be used to acquire exotic stuff or allied dudes, or to pull strings with the Inquisitors of the Chamber or the Crusade forces.
- Using influence to requisition wierd-ass stuff like null rods and needle pistols does give the inquisitor a chance. He's still not going to be fighting magnitude 50 hordes or hive tyrants without problems, but you'd be surprised what you can achieve with dirty tricks.
- Daemon Hunter is a good sourcebook as it contains rules for (human-scale) malleus terminator armour, along with the Pyroclast alternate rank, who are such steaming pyromaniacs they can use an astartes-scale flamer weapon without penalty.
- If an inquisitor is assigned to a kill-team, you'll find missions shift slightly - if it was 'drop in, murder these specific dudes, leave' you wouldn't need him. Inquisitors are required for a missions where:
- You may need an inquisitor's authority on hand - diplomatic-type missions (such as covert meetings with the Tau or Eldar behind the crusade force's back), missions where the Kill-Team is taking direct command of a failing planetary front, or missions where resources such as exterminatus are potentially being deployed (e.g. a tyranid overrun world where the exterminatus 'clock' is being halted for half an hour to allow a kill-team to ****** something vital)
- You need an inquisitor's expertise on short notice - investigations where mission objectives need to be changed (or even determined) on short notice, or where the situation is unknown; the 34th Scintillan has vanished without any vox messages or sign of survivors - find out what the hell happened and do something about it. Equally, a kill-team might be deployed to a world where a genestealer cult is known to be active but the location is unknown - the kill-team largely bunkers down whilst the inquisitor and his minions pin down their targets.
- Operations against Imperial - or even Inquisitorial - people or facilities, where the target would theoretically have some authority over the kill-team.
- Also, your mission options change somewhat. If Malleus Terminator Armour is acquired alongside marine tactical dreadnought plate, teleport deployment becomes a possibility. However, whatever armour the inquisitor is wearing, deployment by cestus assault ram, boarding torpedo or drop pod becomes impossible as the inquisitor simply wouldn't survive the experience; it's physiologically stressful for space marines, let alone unaugmented humans. Planetary drops would be stormraven or gun-cutter deployment, or a HALO grav-chute drop, boarding by assault boat with cutting equipment (like a thunderhawk or shark)
- You're more likely to be operating in non-warzone environments for clandestine operations than simply dropped on a battlefield. Either stealth ops in scout armour or sneaking around a hive world.
- Minions (honour the chapter/first founding, I think?) might not be a bad plan - they give you human-esque secondary PCs you can wander along with the inquisitor with.
- Equally, displacement fields are mentioned in the Horus Heresy, and essentially 'shrink' your bulk and allow an unarmoured astartes to pass for human. Very useful for shenanigans missions. How you sneak your armour and weapons into position is, of course, the trick.. In Blood Games, the team carries a compact teleport homer and has its wargear 'beam in' to lock, load and armour up when it's time to go noisy.