Assigning combat damage, lethal damage, and Might changes

Combat damage is a two-part job: each player assigns damage among the other side's units under strict ordering rules, and only then is it all dealt at once. Nearly every dispute is about the assigning.

Worked example. You attack with units worth 8 Might in total. The defender has Horns of the Dragon (6 Might, Tank), Enthusiastic Promoter (2 Might, Backline) and Chakram Dancer (3 Might, neither Tank nor Backline). Tank must be assigned lethal damage before units without Tank, and Backline after units without Backline (rule 815.1.b and rule 826.3), so the order is Horns, then Dancer, then Promoter. Horns needs 6 to be lethal, and you must assign all of it before moving on (rule 467.2.c.3). The 2 left go to Dancer, which is legal because the damage has run out. Promoter is not assigned anything. Once everything is assigned, all of it is dealt simultaneously (rule 467.2.c.1 and rule 467.2.c.1.a).

The step. Combat damage is the second step of combat, after the combat showdown (rule 466 and rule 467). It happens only if both attacking and defending units remain at the battlefield (rule 467.1). Each side sums its units' current Might, and starting with the Attacker, each player assigns that much damage among the other side's units (rule 467.2 and rule 467.2.c).

Lethal damage. Lethal Damage is a non-zero amount of damage at least equal to a unit's Might (rule 142.4.b). A unit must have lethal damage assigned in full before any goes to a different unit (rule 467.2.c.3). No unit may be assigned more than the minimum needed for lethal while other units remain to be assigned (rule 467.2.c.4). Damage already marked counts toward that minimum.

Ordering abilities. A player must obey every requirement and restriction on assignment if able (rule 467.2.c.6). Units with the same priority, such as two Tank units, may be assigned in any order (rule 467.2.c.7). A unit that has both Tank and Backline lets the assigner pick which one applies (rule 467.2.c.8). A unit that cannot be dealt damage cannot be lethally damaged, so it is exempt from mandatory assignment (rule 467.2.c.10).

Prevention and doubling. Passive abilities and replacement effects that would apply to the resulting damage are treated as applying to the assignment instead (rule 467.2.c.5). Ki Barrier prevents the next 7 damage dealt to a unit, so a 4 Might unit under it needs 11 assigned to be lethal (rule 438.5.a). Lotus Trap doubles damage dealt to a unit: if the assigned damage is modified upward, the assigner picks the minimum assigned value whose applied damage is lethal, and it is not doubled a second time when dealt (rule 467.2.c.4.a and rule 467.2.c.5). If several such effects apply, the controller of the unit being assigned damage chooses their order (rule 467.2.c.5).

Might and bonus damage. Units are evaluated using their current Might (rule 710). Doubling a value increases it by its current value, as a separate effect with its own duration (rule 433.1.a). When a Deal action has several targets, Bonus Damage is added to each target separately (rule 715.2).

Common mistake. "I can spread the damage however I like as long as the total is right." Not so: lethal first, in order, and no overkill while other units remain.