Trust me, who ever wrote that MM's are passive, was doing it wrong. MM's are some of the most active characters out there. If I were you, I'd roll a thugs/dark. With thugs/dark you have a plethora of things to do, solo and on teams. Consider this: With /dark alone you have
1. Darkest Night, which is very much like radiation infection, so you've got to keep that up on your anchor.
2. Tar Patch, giving you a much needed way to keep your foes inside of your Arsonist's burn patches. They will be everywhere, and their damage is insane. This also reduces the mob's resistance, making you hit harder.
3. An AoE res. Take that in for a second. Now remind yourself that it's an AV killer too.
4. Cone Fear. Ever wanted to stop a group in it's tracks? You just did.
5. The one of the best debuffing pets around (rivaling the power of the lich), Dark servant. It heals, it controls, it does all things dark.
6. To top it all off, and as though this set wasn't OP enough as it is, you also get a damn powerful AoE heal. That means 1 button and all of your minions' health jumps.
Plus thugs are great AoE and single target damage, and it's easy to soft cap them with the pet sets (+20% resist and +10% defense to all because you can slot 2 sets in gang war).
Close your eyes and think of this: You're getting close to an AV in a mission where the packs of mobs are +4 and close together. Your trigger happy corruptor accidently pulls a second group. The corruptor takes the alpha for the group he aggroed, instant death. All of a sudden, BAM, the brute gets one shotted. And as the dominator tries to lock them down ends up getting instagibbed himself. The group turns to you. Instinctively, you open up a black hole in the middle of the pack. Two are slightly out of the Black Hole's range, so you send your bruiser to one and instruct the rest of the pack on the other.
You had thirty seconds from when Black Hole's animation was over, and time is ticking quickly. You target the brute and cast teleport. His body lands at your feet...27 seconds. The corruptor and the dominator are both plopped right next to you. 20 seconds. You hit your pet's defensive/follow macro and tap provoke. 17 seconds left and the two that were left standing are now on you. Taking what little time you have left, you cast howling twilight. Everyone is alive and back at full health. 10 seconds. The 4 of you duck into a door way and out of their line of sight. Through the window you're counting it down. 6...5...4... just then you notice the AV was in that spawn.
Quickly you rush to the doorway and toggle darkest night on him, turning the pack's sights to you. Side stepping into the room, you drop a tar patch right inside that doorway. Everything funnels in nice and slow and your group polishes that challenge off easy until finally the AV makes it's way inside.
You use twilight grasp to soak up any of the damage going around. Your tenebrous tentacles hold her in place as your arsonists pulls out the molotov cocktails and lights her up. You and fluffy have debuffed accuracy so badly at this point that the brute gets hit maybe 8% of the time. As she plumets to 50% health, you notice Howling Twilight just recharged. You sneer smugly and whisper to yourself "Time to die, *****". The AV's regeneration plummets and suddenly damage seems to be sticking better. Within seconds she falls to your feet. The group turns around, looks at you and says "Damn, I'm gonna go roll a MM, brb".
Yeah, that's what Thugs/dark is like. You'll be up to your elbows in things to do. Don't let anyone fool you.