The foulest brew
Vellna was not too enthused at having to cook up Rakkrun again, but needs must. Over the millennia fighting the cowardly Raki, Clan Rakidum had developed many weapons to attempt to even the odds against the vile rats.
One particularly sharp-nosed ancestor, Dengrin Dorkonk noticed that the stink of the Skaven changed right before they fled.
It took him close to a century of experimentation to develop the mixture that produced results that satisfied his requirements.
Rakkrun, created from raki skulls marinated in a mixture of bodily fluids in various states of decay, was the foulest thing she had ever smelled.
Old Dorkonk, who had by then developed a tolerance for the stench (or burnt away his sense of smell, depending on who is telling the tale), used to wear Rakkrun as warpaint.
The utter madness!
And while that prevented the rats from approaching him or fighting against him effectively, the stench was so foul that none of the other Longbeards could bear to fight alongside him.
So, rather than shelving the disgusting brew for good, as a relic of misspent youth, Dengrin spent the rest of his years devising ways to use the Rakkrun without needing his 'Gromril constitution'.
By Gazul this caldron smells vile enough to wake the dead.
Despite having an excellent laboratory under her brewery, she would still keep brewing Rakkrun outdoors, as old Dengrin had instructed. It would not do for the stink to seep into the building and up into the brewery.
Dengrin's "sub-optimal" uses for Rakkrun were many and varied, but the most effective of them was to targeting a commander with a flask of the stuff... preferably from a distance.
In the worst-case scenario, where the Rakkrun is not as effective, the stink would overcome the rat's nose, driving him mad with terror and making the subordinates react aggressively to the now even-fouler smelling rat. Either way, the Thaggoraki are left leaderless because their commander is incapacitated or unable to convey orders without being mauled.
In the best-case scenario, the Rakkrun-inspired terror spreads like wildfire among the chittering hordes, leading to a rout and slaughter.
Rakkrun was one Rakidum secret she was happy to see spread around to the wider ranger guild: there was less chance she'd be the one stuck having to brew it herself that way.
And if there was next time, she was making Ansgar brew it himself.
She was old, and with age comes the privilege of not having to smell something this foul.
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@Mayto: Omake for the Karak Izor action.
Wrote on my phone, so probably riddled with typos.
Intended to be Vellna's musings while making Alchemical rat deterrent on behalf of Ansgar.