The monodrone is the weakest and simplest of the modrons, the inhabitants of Nirvana, plane of absolute order and law. Resultingly, the monodrone is single-minded, single-functioned, and completely lawful, utterly following orders from their superiors (usually the duodrones), referring to them when their orders are not sufficient to understand what to do in a certain situation.
As utterly lawful creatures, modrons are not affected by spells that affect the mind (including illusions) or emotions; they are also immune to spells making use of positive or negative material energy. They are also resistant to fire, cold, and acid (save +1, damage -1/die). Death is also not a big problem for modrons, who will simply reform in 9 days as modrons in the energy pool of Nirvana.
Monodrones usually act in groups of 12, led by duodrones or tridrones; 1 in 12 of monodrones lack the spindly arms and have fan-like wings sprouting from a single point instead. These latter monodrones are messengers and can relay messages of up to 48 words perfectly. All monodrones have infravision up to 30'.
Rarely, a monodrone (or higher level modron, but never higher than quarton) for some reason becomes defective (due to age or exposure to chaotic forces) and stops obeying the laws. These rogues are typically hunted down by the pentadrone police force.
Modrons were changed to a strange clockwork race in 2nd edition, and then mostly ignored in 3rd edition, but I like them just fine as they were introduced in 1st edition; they are fully organic, yet fully lawful creature of order and hierarchy - quite interesting as a counterpart to the demons, devils, and devas of the other planes of existence.
Monodrone (Base Modron) Statistics
No. Appearing: 12-144
Armor Class: 7
Move: 6"//6" or 6"/18" (MC:D)
Hit Dice: 1+1 or 1-1
% in Lair: Nil
Treasure Type: Nil
No. of Attacks: 1 or Nil
Damage/Attacks: 1-4 or by weapon type
Special Attacks: Nil
Special Defenses: Immune to illusion and mind control
Magic Resistance: Standard
Alignment: Lawful Neutral
Size: S (3' - 6")
Psionic Ability: Nil
Attack/Defense Modes: Nil/Nil
Level/X.P. Value: II/28 + 2/hp