For reference, here's XComutil's take on Autocombat: (from XComutil.txt)
Automatic Combat Resolution (AutoCombat):
Automatic combat resolution is provided to eliminate the tedium of battles that you think are just too easy. It also allows you to play a new kind of game, AutoXcom, where you never actually fight any battles, but play every battle using AutoCombat.
Using AutoCombat, XcomUtil will update the files with an approximation of the results, rather than requiring you to actually fight the battle. To reduce the complexity of the algorithm, I have imposed a few simplifications. Hand-to-hand weapons, grenades, and extra clips are ignored. Whenever you capture Elerium-115 or Zrbite, you automatically capture a power source. Whenever you capture a ship, you capture some alien alloys and navigation, based on the size of the ship. All other items that are part of the map, such as alien entertainment, are ignored. However, you do capture any equipment carried by the aliens if you win. If you find this to be too restrictive, don't activate AutoCombat until after you have done what you wanted to do or simply play the entire battle yourself.
To activate AutoCombat at any time during combat, just save your game as game number 10 with the name AutoCombat, then immediately abort combat. You can optionally add a number which will be used as a probability threshold for aborting AutoCombat, which defaults to 25%. For example, AutoCombat75 will indicate that you want to activate AutoCombat, but only if you have at least a 75% chance of success, as determined by the AutoCombat algorithm defined in XCOMUTIL.CFG. XcomUtil will verify that the name of the saved game in the GAME_10 directory starts with AutoCombat and that the game date and time match. AutoCombat can only be activated after saving the game, because that is the only way that all of the information about the battle is available for use by XcomUtil.
Saving the game also allows you to reload the battle and fight it yourself, if you don't like the results you got from AutoCombat. If you reload the game and immediately abort combat again, you will get exactly the same results. To really abort, just save the game again as GAME_10, but use a name that does not start with AutoCombat.
The rules on wounding and killing soldiers are designed to allow you to protect your most valuable soldiers. However, they are also designed to make it very difficult to win complicated battles without using a large number of well equipped, experienced troops. Don't expect rookies with pistols to come home. It is possible to gain combat experience from AutoCombat, but it will be distributed randomly.
AutoCombat Algorithm:
The basic success percentage for each soldier with a loaded weapon is 5% for each rank above rookie or seaman. Thus, each soldier contributes from 0% to 25% to your total chance of success in combat.
High reactions and firing accuracy add even more when the damage of your weapons is greater than the average health of the aliens. Similarly, soldiers with Psi/MC skill greater than the Psi/MC Strength of the aliens add to your chance of success. Aliens and other factors, like darkness, reduce your chances of success. To reduce the penalty for darkness, soldiers who carry flares in darkness get a bonus.
All of these factors and the amount they effect your chances of success are specified using StatStrings in the AutoCombat section of XCOMUTIL.CFG. The default abort threshold is also defined there.
If the final success percentage is less than the abort threshold, there will be no combat. If the percentage is 100 or greater you win. Otherwise, your success is randomly determined.
If you lose, the number of aliens killed is based on the amount by which you missed your success percentage. If you win, all aliens are killed or stunned. The soldier credited with the kill is selected randomly. If that soldier is using a small launcher loaded with a stun bomb, the alien is always stunned. Otherwise, the chances are only 1 in 32 that the alien will be stunned. You earn 20 points for each alien you kill and 10 points or each corpse you recover. All alien ammo clips are captured as full clips. Human ammo clips are emptied according to how much they are used, just as in normal combat.
The algorithm to determine who gets wounded is as follows. Each alien can wound one human. The probability of each alien actually hitting a human is the difference between the total success percentage and the success roll, a number between 1 and 100. If the difference is more than 90, the maximum chance that the alien misses the soldier is 90%. If the difference is more than 200, the maximum chance is 95%. Thus, the more overwhelming your force, the fewer soldiers will be killed or wounded.
The probability that any given soldier will be wounded is based on the order defined by the SortStats in XCOMUTIL.CFG. The last soldier in the craft, has one chance of being selected. The next to the last soldier has 2 chances, the one before that has 3 chances, and so on. The Nth soldier from the back, the first one off the craft, has N chances to be selected. That is, if you have 4 soldiers in the craft, their chances of being the one wounded are 10%, 20%, 30%, and 40%, respectively. The last soldier on a full Skyranger has less than a 1% chance of being selected.
By default, soldiers with high Psi/MC skill or very high firing accuracy are moved to the back of the craft to protect them. Thus, it is highly unlikely that they will be wounded if there are many soldiers in the battle. However, any soldier can be killed, regardless of where he or she is placed in the craft.
Tanks are always considered to be the first units into combat and the first units wounded or killed. Each tank receives the wounds that would have gone to the four soldiers it replaces, but tank armor greatly reduces the amount of damage taken. Compared to soldiers, tanks do not significantly improve the chances of success. However, if they are not destroyed in combat, they are immediately repaired when you return to your base.
The damage inflicted by each wound is the average weapon damage of the aliens. The damage reduces armor first. When it is gone, it reduces health, until the human is dead. If a dead human is selected for wounding, another is selected in its place. If a live human has not been found after three tries, the potential wound is ignored.
During AutoCombat, the XCOMUTIL.LOG file records a summary of the battle, along with all Hits (armor damaged, but no wounds), Wounds, and Kills. It also reports Healed when a Medi-Kit is successfully used after a soldier is wounded. The victory points lost because a soldier is killed in combat is 20 plus 10 for each rank above rookie/seaman.
