The drone:
Fly-spy resist spell [OR 15]: 15d6t5 5
Dead average, but still tough to beat on a spell cast. One could also argue that resisting an invisibility spell would be done by the sensors with an OR of 9, so take your pick. Dropping 6 dice loses me 3 hits. Optionally, you could take the sensor's rating into account, adding a dice for each rating (or rating above 1) which in either case would provide a total of 4 hits (sensors are rating 3).
Yeah, I'm not as comfortable with the OR rules as I should be. 15 does seem high with drones, with their kinda crappy Perception skills out of the box. Of course, you could argue that resisting the spell isn't really tied to your vision directly -- LOG+INT. I'm gonna say that the "Drone" classification comes in when one is directly jacked in. That's a nice little bonus, and will probably come in handy for when Zwei joins. We'll go with the Sensor OR of 9. I'm going to think about whether the ratings would add bonus dice, as per the reasons above.
I realize that I have fudged the spirit and office interior. Mercer still has a drone pointed at the latter, so it can see 2 standing metahuman women. They're back near the office wall, so Mercer doesn't have line of sight, though he could theoretically shoot through the window and floor beneath them to get a shot. Let me know if you're interested in that, and I'll work out the penalties. If you want to give me a Perception roll on the drone, I can give you more info on the interior of the office and the women.
On the spirit, I keep forgetting that powers like Concealment and Confusion need to have a Materialized spirit. I'm going to say that since Raziel was also Concealing himself, that the sentry hasn't spotted the source of his confusion yet. That would make Raziel visible to Achak should he reenter the hallway.
Achak blocks! -- or is it Parries? I think the consensus is that when using Block, Dodge, or Parry you're adding a Limit of the linked Skill. So 7 Hits, which is still higher than the Improved Accuracy and Personalized Grip can muster up for the Telescoping Staff to hit. This guy's good, but Achak knows his shit.
Sister Rebecca drops her grenade just on the far side of the conference table, and it goes boom. Without a straight visible line to the carnage it's a little less dramatic, though no less loud, than the last hit. The windows in the conference room that had not blown out are blown out now.
CT3 IP2Achak 17
Q2 8
Q1 6
Sentry 6
Nori 5
Q3 5
Mercer 4
Sister Rebecca 4
Q4 1CT3 IP3Achak 2
Q2 1
Action to Achak, and Initiative for everybody when they get the chance.