Following my post on Elves and Dwarfs in my Adventurer's Tale game. I figured I might as well look at the other side of the coin. While I mostly wanted my monsters to be monsters rather than anything too fleshed out there are three monsters I see as particularly core to a game like this.
The three monster races I consider most analogous to Humans, Elves and Dwarfs are Orcs, Goblins and Trolls respectively and I wanted to present a mostly vanilla version of each while focusing in on what I really think makes each type of monster tick. I didn't want the three races to be opponents of varying toughness. I wanted each to have a unique feel. There are mechanics to back this up but mostly I focused on Goblins as otherworldly vermin, Orcs as an amoral mob and Trolls as stupid creatures with power in their very blood.
All varieties of goblin make their homes anywhere there is a safe hiding place, often in Otherworlds that they know are secret. Although they rarely attack their neighbours outright they are known to enjoy the thrill of stealing, playing cruel jokes and generally tormenting other species. They have an unusual affection for trolls, ogres and giants, though this attention is often an annoyance for the big, dumb creatures. Their love of big folk is equalled by their hatred for other small beings such as dwarfs, kobolds and even cats and dogs, all of which they try to harm as much as possible. They are notorious survivors and can be found in environments all across the world, and even in Otherworlds. Typically the lone goblin is much more concerned about itself than the good of its peers, so they make poor guards or soldiers. Visually they vary greatly but are generally up to three feet tall with grotesque features and skin that can be any sickly colour from orange to yellow or green, often with tufts of different coloured fur, some being completely covered in the stuff.
Rowdy mobs of orcs often raid unprotected villages with packs of warhounds. Sometimes they even form huge armies with archers and war machines but this is usually under the guidance of an evil human, devil or exceptional Orc chief. They are driven by a love of the simple pleasures of eating, stealing and fighting as well as a total lack of morals or care for other beings. Those that live underground sometimes use Goblins or Dwarfs as slaves. Some scholars claim Orcs were once good creatures, but their blood has been tainted with that of demons, or that they were bred into their current form for use as soldiers. Orcs are easily caught up in mob mentality, meaning an army of rowdy orcs are near unshakable in their confidence. Their appearance and colouration varies wildly, some groups having extended lower tusks, pig-like snouts or a more apish appearance. The only things they all have in common are their ugly appearance, amoral behaviour and love of an angry crowd of orcs beside them.
Strong but slow-minded, Trolls live solitary lives wandering their swamp or cave. They are often captured and used as dungeon guards because of their survivability, but they are never truly committed to such a cause. The blood of a troll can be sold to a wizard or alchemist for 10gp or turned into a Healing Potion by succeeding at both a DN10 Craft roll and DN10 Wisdom roll. Troll blood is commonly mixed with the stock of other species by Dark Wizards, usually Orcs or Humans, to create servants. These troll-blooded creatures combine the toughness of a troll with the more alert mind of another species, making much better soldiers.