I considered doing one of these myself, here are the ideas I was playing around with (warning - some of these may not be possible to mod in):
*No special metals, and no mass production for materials above iron level - the idea being to make steel feel more special to gobbos.
*More limited use of stone, gems and glass - Masterwork Dwarfs can make all sorts of stuff from rock, gems and glass, which makes the game easier as it means you can do more with the most common resources in the game - by making the goblins more like vanilla Dwarfs in this respect, it challenges the player.
*More limited farming - I wasn't sure how, but I was considering depriving goblins of underground crops or depriving them of farming entirely. Certainly, I was thinking goblins would lack treefarming.
*Limiting trade - for example, by making it likely they would end up at war with every non-goblin civ, or just making their social skills really bad.
*Clay being an important resource for the goblins, much like it is for the kobolds.
*Making goblins both booze dependent and obligate carnivores.
*Baby-snatching being a major part of the economy - gobbos being weak in combat and slow learners, the gobbos send out baby snatchers to get Dwarf, Elf, Human, Kobold and Orc babies, all of which would be represented in game by goblin "castes" that cannot breed.
*Fast breeding - 'cuz gobbos should be fairly disposable.
*Cattle raiding! Send out expeditions to steal the herd-beasts of your enemies! Would mean that the goblins would have access to all the special domestic animals as well.
*Stolen technology - the gobbos would have access to many of the Orc, Kobold and Dwarf buildings (plus a few others to represent the other races) with an emphasis on low tech. All of these stolen buildings needing blueprints to build. The reactions would be slightly different, to reflect the goblins lack of skill with the foreign technology.
*Demons, necromancers and Uruk Warlords - one of the things I wanted to do was make it likely that your goblins would end up being ruled by some grumpy and terrible creature. Either these would be done as a rare caste or as a very expensive pet that could be brought along. These creatures would have very high social skills to make them likely to be elected mayor, and if possible, made to make them likely to become king.
*Goblin Magic - I was thinking of ideas based around a demon worship theme for this. Blood sacrifice, wicked spells and possibly a link to the nobility (nobles being appointed by the demon-priests, say).
*Slaves - I wanted to have slaves that would be a bit like concubines, only instead of breeding, they would be goblins that could be bought at embark and could be bought from the caravan and would either labour as hauler/peasants or would be war trained (possibly even armoured) and used as disposable cannon fodder.
For example, one of the ideas I had for a goblin embark would be the "warband", which would be 7 goblins, 7 cheap axes and a slave army or war trained slave goblins. Then the player could use "embark anywhere" to use this army to invade dark towers and established sites in order to take kill the inhabitants and take their stuff...
The slave idea may not pass muster with Toady though.
*Slave warparties - like Orc raids, the goblins could send out parties to loot the neighbours. But for the goblins, these raiding parties would require using the slaves of the fortress - basically sending out a bunch of slaves with cheap iron gear to steal resources/technology/babies, if the slaves fail, they either die or run away, and the player loses the invested resources, if they succeed, they are allowed to keep their gear and join goblin society as free goblins (you still lose the invested resources, since the freed slaves go off to found their own fortresses or join other fortresses, but you get booty in return). For this system, I was thinking there'd be a "slave raider equipping" task, where a goblin would take a slave to the workshop, "kill" the slave, consume the armour and weapons and produce a statue like Orc Fortress migrants. Then the "send raid" task would consume say "10 equipped slaves", which would have a random chance of producing booty.
*Typing this all out gives me an idea for another goblin caste - "freedgob", which would be a normal goblin, but they would have say +5 to a selection of military skills. It would add some flavour to embarks and migration waves.
*Other potential goblin caste names - bugbears, hobgoblins, snaga, bogrins, gobbers.
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