As for breeding megabeasts, that didnt work even with the correct tags in 40d. Wouldnt count on too much.
I've recently found that you could/can make megabeasts and powers and stuff reproduce in 40d world-gen by populating a civilization with them in the ENTITY raws. I found this out when I tried to introduce/mod in a civilization based on the GWAR mythos.
I think civilizations automatically override the creature's normal breeding behavior, as I also noticed that, on the other end of the spectrum, the members of my custom mouseman civilization were always giving birth to children one at a time, even though they weren't supposed to be able to have litters smaller than two.
No stray multiple_litter_rare tag?
Just checked for it (using the find function in Notepad), it wasn't there, so that's not the problem.
Did you have the [LITTERSIZE] tag?
Yep, [LITTERSIZE:2:12]
Here's the entire code for them:
[CREATURE:MOUSEFOLK]
[NAME:mouse:mice:mouse]
[TILE:249][COLOR:6:0:1]
[GRASSTRAMPLE:0]
[VERMIN_EATER][PENETRATEPOWER:8][VERMIN_HATEABLE][VERMIN_GROUNDER]
[VERMIN_SOIL][FREQUENCY:100]
[NATURAL][PET]
[INTELLIGENT]
[CURIOUSBEAST_EATER]
[SPEECH:mouse.txt]
[COMMON_DOMESTIC][PACK_ANIMAL][WAGON_PULLER][TRADE_CAPACITY:200][TRAINABLE]
[CAN_CIV][CAN_LEARN][CAN_SPEAK]
[CANOPENDOORS][LOCKPICKER][TRANCES]
[FLEEQUICK]
[COOKABLE_LIVE]
[BODY:HUMANOID_MOUSE_SPECIAL_STUBBY_LEGS:TAIL:2EYES:2EARS:NOSE:2LUNGS:HEART:GUTS:ORGANS:HUMANOID_JOINTS:THROAT:NECK_MOUSE_SPECIAL:SPINE_MOUSE_SPECIAL:BRAIN:5FINGERS:3TOES:MOUTH]
[SIZE:1]
[MAXAGE:18:23]
[ATTACK:MAIN:BYTYPE:GRASP:punch:punches:0:1:BLUDGEON]
[ATTACK:MAIN:BYTYPE:MOUTH:bite:bites:1:1:GORE][ATTACKFLAG_CANLATCH]
[DAMBLOCK:-4]
[SEVERONBREAKS]
[CHILD:2][BABY:1]
[LITTERSIZE:2:12]
[FAT:1]
[EQUIPS]
[BODYGLOSS:PAW]
[SPEED:990]
[GNAWER:gnawed]
[PETVALUE:10]
[PREFSTRING:friendliness]
[PREFSTRING:playfulness]
[PREFSTRING:curiosity]
[PREFSTRING:naivety]
[PREFSTRING:disposibility]
[DIURNAL][CREPUSCULAR]
[BIOME:NOT_FREEZING]
[TRIGGERABLE_GROUP:5:50]
[STANDARD_FLESH]
[MODVALUE:3]
[HOMEOTHERM:10067]
[SPEC_HEAT:4031]
[IGNITE_POINT:10140]
[MELTING_POINT:10150]
[LAYERING:120]
[STOUT]
[SWIMS_INNATE][SWIM_SPEED:2500]
[POPULATION_NUMBER:5:175]
[PERSONALITY:ANGER:O:25:75]
[PERSONALITY:CHEERFULNESS:1O:60:100]
[PERSONALITY:COOPERATION:35:75:100]
[PERSONALITY:DEPRESSION:O:45:95]
[PERSONALITY:MODESTY:10:45:100]
[PERSONALITY:TRUST:50:79:100]
[PERSONALITY:VULNERABILITY:25:85:100]
[PERSONALITY:SYMPATHY:25:79:100]
[PERSONALITY:SELF_EFFICACY:O:65:100]
[PERSONALITY:ALTRUISM:10:60:100]
[PERSONALITY:ANXIETY:0:65:100]
[PERSONALITY:SELF_CONSCIOUSNESS:10:50:100]
[PERSONALITY:STRAIGHTFORWARDNESS:0:66:100]
[PERSONALITY:EXCITEMENT_SEEKING:0:60:100]
I suppose that it could be a result of some of the other weird stuff I did with them (made them vermin, made them pets, gave them an attack with a bottom damage value of zero, the weirdly low melting point (intended to make them kind of cartoonish), the modified body plan, et cetera), but I don't think so. I still think that the small litters were a side effect of making them a civilization.