Currently there are nine failure types. To me, they seem to fit reasonably well into three categories of three apiece: Electrical: Engine Alternator, Batteries, Lights Aerospace: Engine Gimbal, Reaction Wheel, Control Surface Propulsion: Engine, RCS, Tank Slap an "Engineer" or "Specialist" or whathaveyou after each one and you've got three function-based specializations, the exclusion of any one of which could be problematic for any voyage. RemoteTech and TAC Life Support pair wonderfully with this mod, but I kind of assume most people who use this mod also use those. Kerbal Construction Time can compound the problem of rescue missions necessitated by Dang It!, so that's fun, too. Anything where you use a lot of unmanned vessels makes this mod especially devious, and the potential for water or oxygen to leak adds a lot of interesting gameplay. For example, on a recent moon mission, Jeb ran out of fuel in orbit around the Mun. I had to quickly construct a rescue vessel before Jeb's food ran out; KCT meant I would only have time for one attempt. I opted for an unmanned rescue vessel for cost and weight reasons; I just didn't have the rocketry to get two manned pods to the Mun and back easily. Because of RemoteTech, I had to time my rendezvous very carefully; there was not much of a relay network yet. Anyway, the rescue vessel sprung a leak on oxygen long before it reached Jeb. I had to get Jeb home using (a) a vessel with no fuel, or ( a vessel with no oxygen (I had no resource transfer mods). I opted for (, because even though a normal Hohmann transfer from the Mun to Kerbin's atmosphere would take too long to last without oxygen, an unconventional flight path got him back in just under the amount of time his EVA supplies lasted. In effect, I traded some excess delta v for a shorter flight time. That meant a dangerous reentry (with Deadly Reentry/FAR installed of course), but it worked. Long story short, if you like this mod, use the other "hardcore" mods. They function in concert to create problems you'd never expect, and that's really fun. My suggestions: FAR, DRE, TAC-LS, RT, KCT, KIDS, EngineIgnitor, and KesslerKaos, a seemingly abandoned mod that nevertheless appears to work for me so far: http://forum.kerbalspaceprogram.com/threads/74382-Kessler-chaos-space-debris-clouds-0-23-5-WIP-Plugin Great mod, by the way.