In history, homunculi are alchemically-created people, involving some questionable rituals involving the seed of a man, human blood, and a horse's womb. The person created was functionally no different than a man, though said to be considerably smaller, hence the name homunculus, being the Latin diminutive form of homo (man). In RPG gaming however, it is a specific creature created with the Craft Construct feat. Luckily for us, the process by which one creates a homunculus is considerably less disturbing, though one could always choose to involve the more historically accurate version if they wish.
A homunculus is telepathically linked to its master (the supplier of the blood), conveying all its experiences, but cannot speak. This has never stopped me, homunculi can be fun creatures, and talking makes them much more interesting. They also share the nature and alignment of their master, so unlike golems, which are invariably neutral, they actually have personalities that may get them in trouble. It can be fun to watch a player interact with his homunculus, it reveals traits about the character they may never have noticed otherwise. If the construct is under the control of the DM, it can be a way for the DM to comment on the player's perceived nature, though always be aware that a homunculus is unwaveringly loyal to its master, no matter how chaotic or evil they may be.
I think it important to ask a player crafting a homunculus what sort of physical features they would like to give their pet. It says a lot about their opinion of their creations, as well as themselves. Does a character craft himself a handsome butler, or an ugly misshapen lump? Does he make him identical to himself? What gender does he choose, if one at all? What race? Is his homunculus portly or lanky? Dark-skinned or fair? Does he give it hair? While these choices may have little effect in a rule setting, when roleplaying they can provide adventure ideas or opportunities to further character progression, especially when compared with what the character thinks of himself. The player may forget that the homunculus is an extension of his character, but I try not to forget it. It may come in handy.
Between editions, one difference makes itself known: what happens when its master is destroyed. In D&D 3.5, its body dissolves into ichor, while in Pathfinder it instead goes insane, becoming a mindless watchdog for the surrounding area. Some homunculi have been known to recover from this and aspire to more, such as claiming to be the heir to their master's possessions or even their spirit incarnate. A homunculus with a trap the soul gem crafted within it could be an interesting curse that the players could free a friendly wizard from, or better yet, a much more insidious villain. A particularly well-crafted homunculus could even pass for a halfling, so long as it didn't betray the fact that it could fly and had a poisonous bite.
Homunculi can also be used as familiars, with the Improved Familiar feat, making advancing them easier and cheaper. Though a well-funded wizard, (with an accommodating DM) could find ways to build homunculi with more hit dice and then use that as their familiar. The rule that says a familiar must be a normal, unmodified version of the creature normally prevents this from being allowed, but one could always argue that in the case of a constructed being, the terms 'normal' and 'unmodified' are open to interpretation.
That's about all I have to say about homunculi today, if you have any questions or suggestions don't be shy to make a comment. I'm always open to ideas for future posts or A to Z suggestions. Stay tuned tomorrow for "I is for Intelligent Item".