CyberChrist
You caught my attention
I would like to see any Skaven(ratmen) unit for the Warhammer universe made, but in particular I think the Warpfire Thrower (essentially a fantasy flamethrower) would make a great unit
For further details on how they function I have included the description from the Ratbook.

For further details on how they function I have included the description from the Ratbook.
The most feared Clan Skryre weapon is the Warpfire thrower. Dangerous to both its enemies and its bearer, it is capable of incredible destruction. Clan Skryre only employ its most courageous, fool hardy, or mad Skaven to operate these.
This remarkable weapon requires the use of at least two Skaven, one operating the nozzle, the other carrying the Warpconcentrate barrel. One Skaven carries on their back the fuel source, a large barrel of Warpstone Concentrate. The Skaven bearing the barrel also has a small hand pump worn on a harness that hangs across their chest. When the Warpfire Thrower is to be used, the bearer vigorously operates the hand pump, forcing the Warpstone Concentrate out of the barrel and down the hose. This hose is held and directed by the second Skaven who operates the nozzle. This Skaven ignites the Concentrate spraying out, turning the Concentrate into a stream of Warpfire. The effect of Warpfire is terrifying to behold, as its caustic stream sets everything alight as the same time the Warpstone mixture warps and twists and aggravates the existing damage.
This weapon is far from perfect, and is nearly as dangerous for the crews operating it as for the enemy facing it. The mechanisms that control the Warpstone Concentrate must bear the incredible pressure and volatile use. Too much pressure, a blockage in the pipe, or a mislight of the Warpstone Concentrate can have terrible consequences, usually resulting in the catastrophic explosion of all the Warpstone Concentrate, killing its operators and all those nearby.