The Angels of Death Supplement has brought so many new things to the game, from Psychic Disciplines to new “Decurions” for Iron Hands/Imperial Fists/Salamanders to introduction of Cataphractii Terminator Armor to 40K that it is hard to know where to start.
Right out the gate, one of the most significant new additions, in terms of competitive gameplay, is the new Fist of Medusa detachment for Iron Hands (i.e. their own, unique version of the Gladius Strike Force). One of the new special rules (called “Reject the Flesh, Embrace the Machine”) of the Fist of Medusa detachment is that all IH models that are part of it gain an additional +1 to their FNP rolls while within 12″ of an IC from the same detachment.
This means that, combined with IH Chapter Tactics, all non-vehicle models have FNP(5+) “base” if they are within 12″ of an IC and models that already have FNP gain a net +2 to their FNP rolls… thus, a Fist of Medusa Command Squad with an Apothecary gives the entire squad FNP(3+), not to mention any attached Iron Hands ICs (i.e. with the Gorgon’s Chain relic, an IH Chapter Master attached to the Command Squad has FNP(2+)!).
Alternately, if you are able to cast Endurance (say, using a Libarious Conclave) on a Fist of Medusa squad, then the whole unit has FNP(2+). You can even get your “base” FNP from allies, such as attached SW Wolf Priests (they provide their squad with FNP(6+)) or attached BA Sanguinary Priests (they provide their squads with FNP(5+)). Since SWs and BAs don’t technically have the Chapter Tactics special rule, they do not negate IH Chapter tactics by attaching ICs to them, meaning a Fist of Medusa squad with an IH IC and a Wolf Priest attached has FNP(4+) and with an IH IC and a Sanguinary Priest attached has FNP(3+).
There are obviously many applications of all this, but just out the gate here are some of in-game the applications that come to mind:
1 – Fist of Medusa Biker Command Squad with Apothecary/Grav-guns/SSs and attached Biker Chapter Master — The classic shooty Command Squad, the entire unit has 3++ and FNP(3+), giving it better than the equivalent of a 2++ save against anything that cannot negate their FNP rolls (i.e. S10, D weapons, Instant Death weapons, all of which are relatively rare in the game). Add in the top-tier firepower and mobility, and the ability of the Chapter Master to tank with his 2+/3++/FNP(2+)/IWND and T5/4W and you have a very potent unit.
2 – Fist of Medusa Hammernators Squad (from 1st Company task Force AUX) with attached TDA Chaplain and BA Sanguinary Priest with “The Angel’s Wing” Jump Pack Relic — The entire squad starts in reserve, then Deep Strike in, using the “The Angel’s Wing” to mitigate the scatter roll and enemy Interceptor fire (looking at you, Tau Battle-suits). With the Sanguinary Priest’s Narthecium, that gives all the IH Terminators a 2+/3++ save and FNP(3+), meaning they are very difficult to kill with anything that is not S8 AP2 or better (i.e. even BS4 Grav Cannons take 13-14 shots to kill a single Hammernator like this).
3 – Fist of Medusa Devastator Centurions with attached Libarious Conclave of 3 x TDA/SS Librarians — Roll hard for Endurance and, provided you get it and cast it successfully (harnessing WCs on a 2+ should make this pretty reliable), the Centurions have T5, 2W, a 2+ save, and FNP(2+). Against non AP2/1 weapons, this gives them the equivalent of a re-rollable 2+ armor save, making them all but invincible to even massed enemy firepower while they dish out their Grav Cannon goodness. Even against AP2/1 weapons, provided they are not S10 and/or do not have the Instant Death rule, the Centurions still get FNP(2+), meaning for example it takes 21 x BS4 Plasma Gun shots to kill a single Centurion on average.
As you can see, there are LOTs of applications for the Fist of Medusa “Reject the Flesh, Embrace the Machine” special rule. The biggest limitations are, one, that you have to field the Fist of Medusa detachment with at least one Core and one Auxiliary choice to get the benefit (a significant investment that you have to build your entire army around) and, two, that you have to have Fist of Medusa ICs within 12″ plus a source of “base” FNP in the unit to get the most out of these combos.