I've got an idea for a low-rank (ranks 1-3) antagonist and want to screen it through you guys.

He's some kind of crazy low ranking Mechanicus member, angry at the establishment's seeming disgust with the idea of innovation. He's struck out on his own and fled to the underhive, where he builds guns for the local gangs to finance his secret projects. He's obsessed with gravity, and has given himself numerous Maglev and Ferric implants. Combat with him would be speedy, and he could theoretically ****** the guns out of a PCs hands. Raiding his lair might give the party some uniquely fun (if heretical) technology. Thoughts?

Hi Plushy,

first of all, neve ever plan just one NPC to be "the boss fight" unless said NPC is a veritable monster with loads and loads and loads of wounds. Because as long as the NPC is funerable at all (which the NPC must be or the Players will be frustrated) the concentrated attacks of a whole group of PC might wither the NPC down rather quickly. In addition, you need a lot of multi-attack talents to get sure that all of the PC are under pressure. Last but not least, think about the situation where they meet him. If the PC somehow gain the element of suprise (and Players strife for this. It is part of being the cunning (anti-)hero facing the monster-thing) the Tech-Priest might be pretty wrecked after one round. Especially if they get into close combat. Never underestimated mono weapons and "ganging up".

Taking away their guns will not work for two reasons. First, not all of the guns might be "ferric". Second, both of the regarding Talents [Ferric Lure; Ferric Summons) speak about UNSECURED objects (p.116, DH core rules).
Even if you house rule this (or simply disagree on the point of a hand-held weapon being "secured" by the hand of the wielder) you go to far with it: without their guns, how shall the PC harm a floating Tech-Priest? Only a Psyker with an attack power might do the trick now since primitive, non-ferric weapons are unlikely to harm an armoured Tech-Priest.

That aside, a renegade Tech-Priest is a good enemy for a Acolythes of Rank 1 or 2. Perhaps with Rank 3, but be careful here. They get more competent with this rank.

Suggestions:
Accompany him by a number of heretek servo-skulls (or other constructs). This will make a battle against him more challenging since the PC cannot easily gang-up on him. At least, not without punishment (being attacked by servo-skulls with heretek arment).

Consider giving him some heretek las weapons with Penetration:2. Doing this ramps up his threat in regard to lowly armoured PC without negecting the obvious benefits of guard flakk armour.

Make use "Feedback Screech" and think about giving him an excuse to the have the "Combat Master" Talent (so he cannot be outnumbered easily). If you stick with the "he floats!" concept, make sure their are some close combat ground-huggers with him. Otherwise, a close-combat specialist PC might feel "cutted out of the action".

Dunno if such a guy would really fit the image of a "boss" in scale terms, though you really shouldn't be thinking such video game style ideas anyway. Gregoirus is right about the ferric lure being a rather weak power for disarming opponents. Look to the rules for lure and you'll see it only lifts a few kilos, while even a weak pc lifts dozens more, suggesting the pc would get quite an advantage in a resisted str check.

In an open fight, suspect your mechanicus to fall rapidly, in one round, maybe three at the most. In DH RF is NOT a GM's friend. You will find a mechanicus, who likely possesses little more than 15 wounds, will get ripped apart if he's in the open much.

While all this sounds bad for the mech, it can be easily overcome with creativity and cunning. Skilled use of blocking terrain is a must, since your mech is fast he should be darting around behind cover. Ferric lure can easily be a weapon used against the party in disturbing ways. Plan out the encounter zone so the priest has a lot of tricks and knick knacks he can use it on. Sure you won't likely pull a weapon away from a pc, it's possible but very unlikely, but pulling a wrench off a table into the back of a pc's head is on the other hand gonna ring them like a bell. It also never says ferric lure can't flip switches or pull levers, only that the object must be moved towards the user(so a switch or a lever on the ground or control panel could be flipped one way, but a wall mounted switch couldn't).

It's up to you to decide when the party realizes the mech is a threat and engages him, but lessee what should the engagement go like?

KK, here's a concept. You're in the priests large shop, plenty of space to move, he knows the terrain, and there should be piles of stuff and random junk around tall enough to block line of sight. He dodges about, firing any weapons(his bs should stink like hell though so he's not too dangerous) he has and using ferric lure for effects. A pulled lever drops someone through a trapdoor. A piece of equipment comes flying off a bench and bangs someone in the head. One piece of junk at the bottom of a pile goes flying to his hand and the whole pile collapses on a pc. There's plenty of stuff like that you can do.

Just remember, lvl's 1-3, you're looking to do fatigue damage(from being beaten up) and stun damage(from being clonked on the head) during those levels more than hard and painful wound damage so that you're weening the party into the damage system. Lvl's 1 and 2 should be the first and second sessions respectively and level three should be hit in what the fifth or sixth session? That's pretty early into a game so be careful not to kill anybody.