In my opinion, daemons are the heart and soul of the Chaos faction in the 40K CCG. Chaos marines provide the toughness and die modification, but daemons offer a lot of the punishing reactions that make Chaos such a pain to play against. Daemons also provide a lot of the assault muscle for Chaos, from the always-annoying Flamers of Tzeentch to the rightly-feared Greater Daemons. Fiends of Slaanesh is one of those all-star units that perfectly embodies just how powerful and frustrating Chaos can be.
The Fiends’ stat line is about average for a Chaos daemon. 2 toughness is on the weak side but to be expected, and the 3 speed is a nice touch for added blocking potential. The assault ability is when things start ramping up. Assault 3 is pretty mediocre, but when you gain the ability to hit a second unit for 3 damage, you begin venturing toward that distant “2-for-1” promised land. This effect can easily snowball with rallying or charging command lines like Renegade Space Marines (R: After your enemy charges, charge an assault unit) or Discs of Tzeentch (BA (5+): Rally up to two assault units).
For me, the Fiends’ reaction ability is what puts it over the top. The opponent must respect every ability that lets Chaos infiltrate an assault unit at a sector, because there’s always the chance it could be a Greater Daemon. And for Chaos, many of these abilities are reactions that the opponent must play around. Khorne Bloodletters are the most common high-threat unit in this category, but when these units begin to double or triple up at a sector, the opponent is truly stuck between a rock and a hard place.
As if that weren’t enough, the Fiends’ command line lets you remove one of your opponent’s key units from an active sector, or deny your opponent of a flag needed to capture it. At a mere 2+ test, this is quite a powerful tool to have – although sometimes you are stuck with the “first-world problems” dilemma of deciding whether to keep the command line or infiltrate the Fiends.
The only reason you wouldn’t include Fiends of Slaanesh in a Chaos deck is if you hate assault units. Just the ability to threaten an infiltrating Greater Daemon is almost reason enough to run them. With a pseudo-mass-assault ability and quite serviceable die rolls and command line, Fiends hold little downside in exchange for giving opponents a massive headache.