In the Beginning...In the Witch Hunters Codex, they were FAR too expensive to justify, especially considering that Arco-flagellants were available and pretty awesome once you learned how to use them.
In the White Dwarf Codex that came afterwards, the Arco-Flagellants ceased to be part of the Elites slot, and ceased to be elite for that matter. Assassins disappeared entirely from the Codex. That left the Elites slot with Celestians, and Sisters Repentia, basically. However in the White Dwarf codex, their cost came down and they essentially gained the ability that Wulfen now have: Once per game their Act of Faith was that upon dying, they still got their attacks. This made them far more appetizing to use, and I suddenly took interest.. Getting them across the board was a big challenge and that in turn made me start to see that a mechanized Sisters of Battle Force was sadly going to be the way of the future. Having said that I was able to get them to many fights at the end of 5E and into early 6E using the expedient of armored walls to protect them on the way in and sheer numbers.
Even this was more or less too expensive, and 6E ushered in a whole lot of things that made Sisters Repentia fade in excellence again.
Finally, a new actual codex came and with it yet another points cost reduction for Sisters Repentia, but the same dearth of options in the Elites slot as before. After decades of futility it is small wonder that Sisters Repentia have seen little or no interest by the generals of the Adepta Sororitas. With tools in your force like Dominion and Exorcists dominating the points expenditures, and Celestians being a complete joke in the new codex (yet again) the Sisters Repentia now stand as really your only true choice in the Elites slot. I can count on one hand how many people I have seen field them... and I only need two fingers on that hand to do so.
I did however have a day in the sun using the White Dwarf version and so I set about finding a way to make use of this unit now. I have discovered the way to do it.
The combination you need to turn this into a truly terrifying unit is affordable and explodable (meaning it can separate when appropriate when going second to take objectives or to disassemble when the unit is weak to join other units and maintain utility even beyond the life of the Sisters Repentia group itself). The ingredients are as follows:
The Secret Combination
1 Uriah Jacobus
1 unit of 7 Sisters Repentia
Let's Start With The CanonessShe is maligned among internet personalities and long threads have been devoted to this negativity. I have been in the maelstrom of some of those discussions defending her, which is how I know. Even as far back as the White Dwarf "Codex" wherein she was improved a bit, my use of her Sororitas Command Squad to good effect was questioned again and again. That squad at the time was actually much better than people gave it credit for, but of course all they saw in it were T3 models that die the same as everyone else and were expensive. As usual, I was the odd duck who found use in it.
In the new codex, she is a very affordable HQ with completely unremarkable "Space Marine Captain like" stats, maybe slightly worse but the price is right. She is not a combat beast, but she does buff her unit with Hatred as her once per game Act of Faith. She also gets the effect of the old Book of St. Lucius making her Stubborn (and therefore obviously her unit). BOTH abilities, largely, are emulated already by Uriah and the Priest being Zealots, and in Uriahs case, the banner he carries, which might be a good reason why people haven't really gravitated to this particular build or seen her value. Sisters Repentia are already Fearless as well. Yet she is pivotal to the units success.
So then why take her?
She is important because she can take two items you will want. The first is the Mantle of Ophelia which St. Celestine cannot have, and the second is a plain old Rosarius. You literally need take nothing else on her. What this does is allows her to become an Eternal Warrior. In addition, it gives her the 4+ invulnerable save. These two things make her the perfect "tank" for the unit. Her purpose in life is not to kill anything, it is to die for her cause and become a martyr. How appropriate, don't you think? In combat, when wounds are normally being allocated, she will be the first to take wounds, but she will be equipped to take any STR of wound and any AP. Even a WraithKnight won't kill her before the Sisters Repentia get to strike, as you will see. In fact it is quite likely that none of the Sisters Repentia will die no matter the enemy they strike, while the Canoness lives.
To make sure of this we add the next ingredient.
The Priest upgrades the Sisters Repentia greatly. Youu gain Zealot, meaning re-rolls to hit on the charge. That is important. To add to the picture, he will take the Litanies of Faith, which is why Uriah isn't enough for this squad to do its work, for he cannot take it. The Litanies make your Acts of Faith and War Hymns instantly successful when normally you would have to roll a LD check to pull them off (Priest LD is only 7). No rolls necessary with this guy on the job. No chance for failure. Pretty big deal. He himself requires no armaments. After all, look at the unit he is attached to. If they fail in their duty when re-rolling hits and wounds, no amount of points wasted on his puny butt will matter. The Priests Warhymn of choice on the charge will be to re-roll wounds, so that the units already incredibly potent strike on offense will be compounded against tougher opponents like WraithKnights.
Uriah Jacobus Ascendant
The next ingredient is Uriah. Now it is debatable whether he is a must include in general, but Uriah Jacobus shows up in a lot of competitive Adepta Sororitas lists, so taking him would be a relative normality in the list you probably would take anyways. More common would be St. Celestine (or both) but not in this case.
Uriah is perfect for his job in this unit. He comes with Indomitable will as his Warlord Trait and so you would choose him to be your Warlord in this instance. The net result is that his unit gets a +1 to their 6+ Shield of Faith saves! That means that the Sisters Repentia are now getting a 5+ Invulnerable save to replace their complete lack of armor. To make this more impressive, he would choose in melee to use his War Hymn to re-roll all saves. As he is also Protector of the Faith, he will allow his unit to use their Act of Faith one additional time for free, so he acts somewhat like a Simulacrum Imperialis for the unit which would do the same thing and Sisters Repentia normally cannot take a Simulacrum Imperialis, so this is quite useful.
The Banner he wields makes the units within 12" Fearless and the BIG deal with him is that he gives them all Counter Attack which as you will see, serves this unit devastatingly well, and it would serve the Battle Conclave well if they too were near him...and they should be, forming a wall of very mean, very fearless and very deadly killers.
The final ingredient is the Mistress of Pain and her Sisters Repentia. The Mistress is important because you will need her to accept challenges. Worst case, she can also be used to pass a wound off from the Canoness, as the Canoness will always be leading the charge here. Always.
The Guests of Honor
The 6 Sisters Respentia come with an Act of Faith that gives them a 3+ Feel No Pain save in the Assault phase. Because of the way the Act of Faith is written, this is activated at the beginning of the phase and therefore affects them even against Overwatch. The unit itself whallops opponents, pumping out 24 STR 6 AP 2 chainfist attacks. The Act of Faith can be repeated thank to Uriah which mans that unless the enemy is using something that is STR 6, that Canoness could perhaps survive 36 wounds on her own at STR 5 or less!
Putting it all TogetherWhat does it all mean? It means that whether you charge them or they charge you, this is what will happen:
The enemy will likely have initiative and go first or at the same time as the Canoness. The wound pool from the enemy will be allocated to her first because she led the charge. She is an Eternal Warrior. Because of the War hymns, the Canoness will get a 3+ re-rollable save against these wounds! If they are of a sufficient AP, her saves will be a 4+ re-rollable with the ability to pass off one to the Mistress or even to Uriah if necessary. Uriah and the Priest all have 4+ invul saves (again, re-rolling failures) so this represents a pretty significant number of saves that should result in the unit taking no real damage of note barring fantastically unlikely rolls. the 3+ Feel No Pain is just insult to injury.
The next thing that will happen is the Canoness will swing, re-rolling to hit and wound, and then Uriah and the Priest alike, along with the Mistress of Pain if she was able to be preserved. Her Neural whips go off of majority leadership, and have shred if the majority is 8 or less, so this is a pretty mean weapon at AP 3. Finally, the 24 STR 6 AP 2 attacks re-roll to hit and to wound. the sheer volume of attacks and wounds suffices to demolish nearly anything.
This will happen even if the enemy charges because of Counter Attack. If the enemy is an Imperial Knight, or anything else really, there simply won't be one at the end of the turn. No unit in 40K can do much about Stomps, but with that many re-rollable saves, the only thing you'r really worried about on Stomps is the roll of a 6. Yup it happens but that would be true for any unit, so no sense bemoaning that. It's more a reflection of the Knights awesome nature than the Sisters Repentia failings.
But, But, But...All of this should impress any opponent you use it on. The standard argument against this will always be the same: "Yes but how do you get them there".
Fortunately there are answers to that questions. Consider that the question isn't entirely meritorious to begin with, Many excellent armies, the Wolfstars among them, are assault oriented and have strong assault elements in any event as part of their key strategy. Chaos Cabals in Khornate Hound packs and Daemonkin in general as well as Tyranids and Bullyboy Orks. So in many cases you'll never have to worry about that, because many good forces have no choice but to close if they wish to survive the Exorcist barrage and the like. Also, objctives are a thing and in any ITC tournament, standing back all game simply won't be possible if you wish to win.
Lets assume we are talking about that percentage that does indeed have the means to stay away and just shoot you off the table given the opportunity. There are enough of them to address it. Against them, the answer isn't much more complicated: Move flat out, preferably to cover in round one and get out round 2 or possibly sooner if you think terrain will permit. The Sisters of Battle do have the means to shoot the enemy as well, and it is a rare army that will ignore 3-4 Dominion Squads on their doorstep to deal with a melee threat that will get their eventually. If they do choose that route, the rhinos and wreckage should provide the unit plenty of space to go from cover to cover if you plan accordingly and the Dominion can feast on the enemies decision.
One underlying assumption when using this unit is that you are committed to playing as an armoured column and not primarily on foot so there will be many chances to take advantage of all that mobile cover as you approach. You just have to keep the pressure on up front long enough to get them there, and we have those tools.