Maim
When this unit rolls Combat skill dice, the total damage rolled is reduced by half, then roundedRoundingIf a game effect requires players to round a number, but does not specify how, it is rounded down. down. This effect does not apply to true damageTrue DamageTrue damage cannot be prevented or reduced by abilities unless they specifically affect true damage. True damage ignores any bonus HP and reduces the unit's HP instead..
Is damage rounded down per die or cumulative total of all damage dealt by Combat dice?
The damage is reduced for the total amount of damage rolled. You sum the value of all rolled Combat dice and reduce it by half (rounded down).
If a unit rolls 1 damage on it's Combat skill dice, how much damage does it deal?
The 1 is halved to 0.5, which rounded down is 0. Therefore, the unit will deal 0 damage.
How does Maim interact with rolling Combat dice in 
DefensiveRange: N/a. This form represents using the Combat skill to prevent damage instead of dealing it, or setting up other defensive skills such as Heavy Armor. battle form?
Maim only interacts with damage dealt, so you may still freely roll Combat dice and place them in active slotsActive SlotDice placed in active slots are referred to as active dice. An active die remains in its slot until you remove it as described in its skill line's reference sheet or at the end of battle..
If an adventurer with Maim rolls skill dice alongside Combat dice is the damage of these skill dice also reduced by half?
Only the damage dealt by Combat dice is halved, all other damage is unaffected.
SourceWhich Combat dice does Maim affect?
Both white and black Combat dice will be affected by Maim.
Source