Was just looking through some of the info released and was drawing some threads, that may be tenuous but might paint a picture as to what we're seeing in the last two videos of the reveal; the mentioned underworlds army and the final tithe of bone video. Now you may have to bare with me here but i think some of this lines up so we begin here:
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so the warband has bows and melee weapons
It mentions directly that the curse of the Katophrane followed them, guessing Stormcast narrator, out of Shadespire
which brings us here: https://whfb.lexicanum.com/wiki/Katophrane
read the society section for ticking the box here on the weapons.
Next we have old ugly:
looks pretty similar to:
In design at least this seems too close to not be the same headdress even if it is now a gruesome morph by comparison.
So by now i'm pretty confident that the new warband is the Katophranes, as for how this lines up with the tithe of bones video we have this character: https://whfb.lexicanum.com/wiki/Makesh
could this be our main contender as who is being portrayed here?
Katophrane: yep
Wanabe necromancer: yep
Potentially twisted by Nagash and brought back to undeath: I can't see why not
Smashed by sigmar: ? jury is out on that but i certainly see a big old whole in his narrative that could be exploited and filled as such
Escaped from a prison: ? Maybe depends on what you class as a prison, shadeglass? stormvault? death itself? Temple he died in before his soul flew off?
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So in conclusion new army/extension to nagash: Battleome Katophranes + a warband to go with them?
Even if the battletome part might be a miss, which for sure i can accept, seems close enough that the warband will be the Katophranes possibly lead by Makesh. But hey it's all speculation here right...