Ok, so this may seem like a stupid question, but I've seen people talk about a "last dwarfs alive" scenario where there are no Dorf civs on the map and all you get is the first 2 migrant waves...how do you do this? Whenever I create a map that has no Dorf civs, I can't play DF mode. Only Legends and Adventure mode.
In order to create this scenario, you must generate a world in which there have been dwarven civilizations, all of which are destroyed before the worldgen history is finished. This is probably easiest to accomplish done by a.) creating a world that is overrun with cursed regions, b.) creating a world with obscene amounts of titans, megabeasts, and semi-beasts, c.) opening the entity_defaults and lowering the number of dwarves a civilizations begins with (from 100 to 2, for example) or d.) a combination of the three. Generating such a world may take a couple dozen to a couple hundred attempts.
If you take the a.) route, make sure that there are some nuetral (not evil or blessed) mountains for the dwarf civilizations to start in.
The number of migration waves and dwarves that arrive for the first year is random; it is not a mod, but how the game automatically starts a fortress, before checking to see if there is a mother civ. After the first year, you will not receive any more migrants.