A mission, combat or battle are the same thing: a tactical fight played out on a grid of squares.
The foes for the fight are drawn from cards at the start of the mission. Each monster faction has a deck of available monsters, that starts with two basic monster types and increases as calamities occur. Each card drawn normally adds one of that type of monster to the battle, except that as calamities occur, some cards will be upgraded to "Monster II" and "Monster III". These add 2 or 3 of the indicated monster, respectively.
The number of cards drawn depends on the 'mission type. It starts at with the enemy force strength. Then add 1 for each full chapter you have completed in the current campaign (ie, if you're in Chapter 3, add 2), and modify for the mission type below.
Some missions, especially scripted chapter-ending ones, may be interrupted by cutscenes. These do not end the battle. Abilities that may only be used a limited number of times per mission do not get reset until the heroes reach victory or defeat.
- See Combat mechanics
A battle that begins whenever an enemy army moves into a territory occupied by one or more heroes. A Defend against incursion event is triggered, and then a battle automatically begins in which the heroes goal is to survive for a set number of turns. Various bonuses can be had during the battle if the heroes have completed Prepare Defense jobs ahead of time. Victory removes the enemy force from the map.
Victory removes the infestation but does not destroy the enemy force.
Fight a Retake the Station mission when you attack an incursion force instead of waiting for it to attack you. Victory condition is "Defeat all Foes".
Some events result in the heroes being thrown into an unexpected battle. The number and composition of the foes and the victory conditions are determined by the event, and may be just about anything.