Plague Runeword is the weapon type Runeword in the first Ladder season of Diablo 2 Resurrected. The weapons it applies to are Claws, Dagger and Sword; it has three slots in total and requires the Cham+Shael+Um Runes combo. Plague as one of the Ladder Runewords added in 2.4patch is not available to non-Ladder mode players.
Plague Runeword is a good fit for Poison Necromancers that use Daggers as their weapon because of its obvious buff to builds that use Poison as their main elemental attack. Plague yields high value as the only Runeword that reduces enemy resistances and destroys poison immunity. Players can also buff elemental damage from its Cleansing Aura, and achieve high melee damage through the critical strike and open wound buffs.
The best base weapons for Daggermancers to use Plague are Cinquedas (Exceptional) or Fanged Knife (Elite); Mercenaries are Phase Blade, Conquest Sword and Mythical Sword (Elite).
For the Runes combination of Plague Runeword, the farming locations are as follows:
Cham: Hell Secret Cows, Act 4 Hell and above, which takes Hell as the lowest difficulty.
Shael: Nightmare+ Countess, Normal Hellforge and Secret Cows, Act 5 Normal and above, which takes Normal as the lowest difficulty.
Um: Hell Countess, Nightmare+ Hellforge and Secret Cows, Act 4 Nightmare and above, which takes Nightmare as the lowest difficulty.
As the highest level Rune, Cham is not easy to acquire. If you're having trouble farming, buying directly on MMOWTS will be your best option. You can buy cheap D2R Ladder Items here, including Runes, Gear, Runewords, etc. to enhance your build and advance your Ladder process.