Warpstone Flux Rating: ⭐️⭐️⭐️⭐️
4/5 stars - just. The Primarch of the Death Guard casts his sinister shadow over the Second Edition of Horus Heresy with malice and strong rules.
Background.
Of all of the Emperor's sons, Mortarion had the toughest upbringing of the lot. Cast on Barbarus, he lurched from being adopted by a necromantic giant, through to escaping and forging an army to take on the darkness out of the brave souls that were preyed upon by the dark overlords of that world. He failed. The Emperor had to save him and slay his would be adoptive parent. The darkness never really left him, and Horus persuaded him that the Emperor was really just another tyrant to bring to justice. Mortarion and his own sons paid an exceptionally high price for their heresy.
Strengths.
The warlord trait (Sire of the Death Guard) is an army boost that ensure his sons don't worry about Fear or Shell Shock. This is excellent and harks back to first edition very nicely indeed. The added assault phase reaction is fine.
Mortarion comes with the usual armour (which surprisingly provides no other boons). Poison, rending, and flesh bane have a much reduced effect thanks to another rule though. His weapons are fine without being outstanding. That scythe does have reaping blow (2) though - so ensure his targets are nice and tightly packed.
His stat line is mostly good, with the exception of initiative which will see him swing last most of the time - this is a significant negative. This is made up for by the 4+ It Will Not Die rule, along with a small list of other special rules like adamantium will at 3+ (beautiful and fluffy!) as well as hatred of psykers.
He signature move (sic) is the Shadow of the Reaper. This allows him to redeploy up to 10 inches - intervening terrain be damned - during a shooting phase AND he can make a disordered assault right after it. I cannot underscore this ability enough. Mortarion has some of the best movement among his brothers. This will allow him to easily choose his targets, and herein is his purpose: he is fundamentally a killer that gets to choose his targets. Select a big blob of back line enemies perhaps? Grind that contemptor to spare parts? Take your pick. Literally. With this ability, you can afford to choose your targets every time. Take him with a unit of terminators or Death Shroud and you're good to start turn 1 with them, but then you will want to depart and get him doing his own deadly thing.
Weaknesses.
Like some of his other brothers, he is not quite the dueling super star. In fact, he is wasted in this role as much as Alpharius might be and is probably not in the top half of his brothers overall either. Hence he has to be played to his strengths. To be blunt: he has to select his targets and chew through them quickly and in succession. Use an escort to begin with, and go from there. Don't get into Primarch duels with him. He is utterly wasted doing that, although given his toughness and It Will Not Die, he might be able to tar pit them for several turns in the hour of need.
Overall.
Mortarion is strong against large mobs, and backline targets. In fact, he's great against everything that isn't a Lord of War or his brothers. Plus he has army wide boosts and 7 juicy phosphex bombs to let rip (try not to forget about those bombs!).
Difference to First Edition.
He no longer re-rolls It Will Not Die, nor is he totally immune to poisons, nor spreading stubborn to his sons. Arguably he is therefore a tiny bit weaker in second edition overall. But it doesn't matter. He will still smash through a unit per turn when played right.