Why XCOM’s Random Results Sometimes Aren’t (and You Should Play on Ironman)

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I started out playing Firaxis’ XCOM: Enemy Unknown on “Classic” difficulty with “Ironman” disabled. I had this idea going in that I was going to inch rather than sprint through the game, reloading if I lost soldiers, like whittling slivers from a wood carving or lingering over each sentence in an anticipated book. Missed shots? Botched moves? Wounded or incapacitated soldiers? No problem. But permadeath, no thank-you, at least not the first time through.

It’s a slightly obsessive way of playing a turn-based tactics game, granted, but one that’s designed to ensure you’re always putting your best foot forward as you work through the game’s strategic layer, safeguarding leveled-up soldiers and snowballing your capabilities. You pay for the luxury in time and iteration — how repetitive it feels depends on the game’s unpredictability each time you draw back the hands on the clock.

(MORE: How XCOM: Enemy Unknown Is Like Bowling)

In XCOM, the more you’re inclined to alter your squads’ moves and actions when reloading from a save point, the less automatic each scenario feels. Obvious, right? If you take a low odds shot instead of hunkering down (a defense-bolstering option), different results. If you choose to reload instead of spending your clip’s last shot on overwatch, different results. If you zig instead of zag, different results. And if you’re the sort of player who never does the same thing twice when reloading, what you experience will always seem unpredictable, guaranteed.

But let’s say you’re playing through a sequence of events in a scenario that leads to one of your soldiers being flanked by a sectoid (XCOM’s “gray-skinned, black-eyed” aliens) who fires and scores a one-shot kill. If you reload, then perform each move and action in XCOM exactly as you did before from that point in the scenario, you’ll get exactly the same results.

I don’t mean sometimes or mostly, but every time and precisely the same, from misses to hits, damage meted out or incurred, where your opponents go and what they do, and so forth. Execute the same moves a dozen times in a row and you’ll have a dozen identical replays, right up to and including the sectoid shot that puts the soldier you were reloading to save down. As The Doctor might say, some events are fixed points in time: In XCOM, those fixed points become tantamount to saved games when played as re-enactions.

There’s a reason for this. Technically speaking, it’s because XCOM randomizes its numbers from a seed that’s saved at the outset of a scenario. That seed determines what happens thereafter, and once you’ve memorized a certain play sequence, if you choose to repeat it, it’s doing so in essentially non-random terms.

Bear with me here. Random numbers on computers aren’t truly random, they’re actually pseudo-random, because computers are deterministic. The best they can do is generate sequences of numbers that appear random (well, unless you’re hooking them up to geiger counters connected to radioactive material, but that’s another story). In most instances, pseudo-random is random enough. The purpose of randomization in games is to create unpredictability (the more predictable a game, the less interesting and game-like it tends to be). You might describe a game like XCOM as a predictability refinement simulation, where your choices — add this skill, equip that piece of armor, research a given alien technology — chip away at the game’s arbitrariness.

The random numbers in games like XCOM are sequences of non-repeating numbers, but they’re not plucked from the ether — they depend on a seed (usually a number) to initialize the sequence. The first time through, the numbers will appear random (and in XCOM, unpredictable from your vantage) because you’ve never seen them. But load a saved game, which generates its random numbers from the same seed, and if you repeat the same actions, the scenario will draw upon the same sequence of numbers and produce the same results each step of the way.

A problem? Not necessarily. In fact when I asked XCOM creative lead Jake Solomon about it, he said random number generation in the game works exactly as intended:

We use synchronous random in combat so the player can’t just reload when they miss a shot. Now, obviously there are ways around this, but this is a decent way of ensuring that the player’s choices do matter.

What Solomon and the design team at Firaxis are trying to prevent is the sort of play-through where you save and reload for every action to get the results you want. Did one point of damage instead of two? Reload. Didn’t hit that sectoid peeking around a corner? Reload. Can’t find the best position to get the highest-percentile shot? Reload. That’s no way to play a game, or at best it’s a tedious one. What’s XCOM without risk and consequences?

There’s a way to prevent repeating yourself, to tie your hands behind your back, so-to-speak. If you enable “Ironman,” the game autosaves as you go, locking in every action the moment it occurs. Whatever happens, happens. There’s no saving to a separate file or reloading. It’s bulletproof, too: Flip the power switch on your system after botching a maneuver or losing a soldier and when you power back up and load into the game, you’ll be right where you were, post-undesirable outcome.

Playing in “Ironman” mode solves XCOM‘s predictability “issue.” There’s no going back and second-guessing what you did, no sussing the random number generation seed’s sequencing and experiencing the same results if you enter the same commands.

This, in my view, is how to play XCOM, both for its challenge and the unpredictability guarantee.

MORE: XCOM: Enemy Unknown — Definitely Not Halo Reach 2


Hmmm, I didn't save games during encounters... only before. That way if I wanted to reload, it was a newly generated map and not a repeat of the same exact game.


I've been a game developer for most of my career and have worked on Jagged Alliance 2 (which is similar to XCom).

Seeding an encounter and saving it is a very common practice with turn based games, and having just completed normal mode without ironman, I took advantage of this. Usually I would save after taking out a group of enemies, then advance to the next encounter. If things didn't go as planned, all you have to do is do alter your orders. For example, say your first action is to shoot with your heavy (but you miss), then shoot with your sniper (and hit). If you reload and attack with the sniper first, you might hit -- then do it again with your heavy -- it also might hit. It is also possible both will miss as well. Sometimes you have to be creative to save your important soldier from certain death or to make the critical capture.

Veso Mitev
Veso Mitev

There are other games that set the random seed as well.

I remember back when Warcraft III came out, I was tweaking with the editor, making some sort of a mini cut-scene.

In the cut-scene a hero was attacking zombies. He had around 10% to cause stun. Every reload the stun was delivered on the 5th hit, and I reloaded tens of times for testing purposes.

It matches the same experience here - since the scenario cut scene was exactly the same, it seems that the seed was also exactly the same.

Also, I believe Blizzard tweaked the random in the game so you don't get too many hits with scoring stun combo and at the same time, you don't get too many hits without scoring stun at all.

There were also some other TBS games with fixed seed, yet I cannot remember atm.


Seriously, that was way too long an article about a minor design function. How about including more game facets? BTW IT IS A GREAT GAME AND SO MUCH IMPROVED ON THE ORIGINAL SERIES!!!!!


Wow It's definately a good game, but in my opinion the only thing improved from the original is the graphics.

Tjalfe Arcturus Trym Svendsen
Tjalfe Arcturus Trym Svendsen

 no its a shit game and it destroyes the idea of the old xcom -_- could write for ours how the ai, control scheme, camera control, turn movement design, only 1 fire per turn design, etc etc etc. is totally fcked and doesnt have much to do with the xcom serie at all, the only thing it have in comment is the story and that its turn based and on a grid... everything else have nothing to do with the old xcom games -_-