Pox Riders are another steed of Nurgle. Whereas the Plague Drones are the aerial deaths from above, Pox Riders are the
charging hopping cavalry of RIBBIT! Doom. You see Pox Riders are Plaguebearers who have successfully tamed a Plague Toad and often used these giant frogs of death and pestilence to hop over entrenched enemy lines, crushing and maiming anyone who gets in its way.
The ability of the Plague Toads to jump really high and reach the tallest areas or breach the highest fortified walls has been seen as useful for the forces of Nurgle. Those fortunate toads who have not succumbed from Nurgle's daily depressed-filled, emo rage are often recruited into the arm forces of the Death Guard as their quick speed compensates for the traitor legion's really, really slow movement speed.
Most often than not, Pox Riders are often used as scouts to infiltrate behind enemy lines. Its natural camouflage of brown shit and snotty green, as well as the ability to jump to unreachable places, makes it great to hide behind bushes, swamps, forests and even deserts (The only biome it fails are anything to do with snow, since brown and green stand out a bit too much in a blanket of white.), thus the usage for Pox Riders as infiltrators are highly valued by the forces of Nurgle.