I've not exactly thought this through yet, so I really doubt this will be any kind of comprehensive list. The first thing that came to mind, was to go through the special abilities/weapons, and think up at least one way of using them for each.
Blood Razor: It's a magical weapon, and Mortenebra could really use a few of those. In addition they get some very useful attack options, though they only function during their activation. This will free up the Warwitch Sirens to power boost, and remove that hard decision between boosting and clearing out models.
- Blood Mist; Detonating victims to create 3" clouds, seems like a useful option. This ability is enhanced, by not being limited to enemy living models, which means that the witches can stab each other. Stabbing each other creates clouds, and gives Mortenebra a place to hide. If things aren't going well, this might very well save her.
- Death Strike; Very useful ability, though quite weak. This allows Blood Witches to detonate living models, and cause damage rolls on nearby enemies. During Recalibration, this ability will devastate light infantry, and take it's toll on medium infantry as well. In addition it has synergy with "Blood Shadow".
- Dispel [Hag only]; Dispelling upkeep spells is fun. Don't be afraid to hit your own models, as getting rid of a debuff is often worth a bit of damage/loss. No need to think up a way of using it here, as it's a great tool to have available.
Entropic Force [Hag]; No real reason to invent new ways of using this. It's why I'm bringing them in the first place. Do make sure, that you get her in range before Threshering a unit of Kriels.
So what can they do...
- Defend Mortenebra
- Remove Upkeep spells
- Remove Tough
- Open lanes
- Tie down shooting units
- Remove key models from play