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Xenonauts 2: Ground Combat

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For Xenonauts-2 we are retaining all the core elements of the ground combat in Xenonauts 1, but making the experience more freeform and less repetitive. The classic "Time Unit" system is not seeing any fundamental changes but more varied missions and environments and more exotic equipment should keep it feeling fresher for longer.

The topics of discussion are:

  • Mission Types & Mission Mix
  • Alien Composition
  • Breachable UFOs
  • Improved AI
  • Further Changes

Mission Types & Mission Mix:
One of the biggest complaints with the first Xenonauts was that the missions and maps repeated far too frequently - and this was entirely warranted (even though Xenonauts had over 100 maps in it). The average campaign of Xenonauts probably involved 80-90% UFO Crash Site missions, the only variation being the size of the UFO. Ironically, a player that was doing well could actually shoot down all the UFOs before they could spawn anything else ... so ALL they got was Crash Sites. It's not difficult to see why this made the game a bit repetitive!

In an ideal campaign, we'd expect a player to fight approximately 20-25 missions. This would include the final mission and roughly 4 terror missions, 3 alien base assaults, 2 base defence missions and the remaining 10-15 being crash sites (there's planned to be eight different UFO types in the game, all of which are new designs). We'll be introducing terror missions and alien base assault missions earlier in the game, and we'll be adding code that tries to pick biomes and maps you've seen less frequently where possible.

We're also adding a bit more content in the form of the new Boreal and Tropical map biomes, and a new Eliminate VIP mission type. Terror missions have been updated because they often felt like a chore in X1 due to the lack of strategic rewards for their completion, so we've added some alien bombs to the maps which award Alenium on victory. Taken together, we expect these changes will make the campaign quite a bit more varied than the first game!

Alien Composition:
I prefer the classic X-Com model of having UFOs populated by a specific alien race to the XCOM model where every mission will contain a mix of aliens of different species. However in X1 we ran into some limitations - for example, if Sebillians aren't very accurate and prefer short-range weapons it becomes pretty easy to fight an entire map full of them. This is part of the reason the aliens in X1 felt somewhat generic; they all had to be reasonably capable of fighting at all ranges.

In X2 we're going to maintain the distinction between the species but expand the roster of each race family a bit so more interesting units are possible. For instance, the Sebillians come in a standard variant who are fairly capable soldiers but they also have Brutes, which are bigger and tougher and carry a heavy machinegun, but are easy to hit and relatively inaccurate. They'll also be supported by small numbers of Mantids, which are small insectoid aliens that are weak but have good aim, and are backed up by Reapers in terror sites. Hopefully this will make each individual mission a bit more varied compared to the equivalent in X1!

At the moment the three race groupings are the Psyons, the Sebillians and the Wraiths / Androns, and if goes well in Early Access we'll likely be adding a fourth that appears a bit later in the game. 

Breachable UFOs:
The UFOs in Xenonauts 2 are now being designed by the same artist who designed the UFOs in the first Xenonauts. Earlier in development we experimented with fully-destructible grey box UFOs, but even though they offered gameplay advantages over the X1 UFOs they just didn't get people excited about seeing what was coming next. The air combat in particular looked pretty bad when every UFO design was a fairly simple geometric shape.

We are however also going to attempt to fix the only major problem with the UFOs in the first Xenonauts - their indestructible hulls did not allow you to create additional breach points so every assault involved going in through the front door. An impressive mod for the first Xenonauts called Fire in the Hole (packed with Community Edition) laid the groundwork for our planned UFO destruction system; there's specific points in the hull of each UFO that can be destroyed and if you inflict enough damage on them (the C4 charge is good for this) then this removes a section of the hull and gives you an alternate entry point.

Although this system hasn't been tested yet, we're hoping that we can visualise these weak points by showing areas in the hull where the outer hull plating has been broken. In an ideal world different breach points would be available in different missions so the player has to vary their tactics a bit. This is all a bit complex because of the wall hiding system we use for our UFOs (where the hull vanishes as soon as you can see inside the UFO) but if all goes to plan our new UFOs will offer the best of both worlds.

Improved AI:
The next area of planned improvement to the original Xenonauts is the enemy AI. I've always thought the AI in the original X-Com from 1994 felt pretty solid despite the age of the game; the aliens moved around a lot and often did smart little things like checking outside the doors of their UFOs for enemies. The system that powered this was actually pretty simple, and we're going to be adapting it for our own use. If you're curious as to how it works, it's explained below - if not, all you need to know is that the aliens will be more mobile than before and will pick more interesting locations to end their move in!

The system works by manually placing AI waypoints into the map. Aliens will randomly choose each turn whether they want to go into overwatch mode and remain in place, saving all their TU for reaction fire, or go into movement mode and or attempt to move to a nearby waypoint within a certain range. The chance of selecting each mode is dependent on how aggressive the aliens are; e.g. a melee alien like a Reaper will almost always be choosing movement mode.

When any alien spots a Xenonaut unit, the system above is abandoned and for the remainder of the turn all TU is spent either trying to kill the hostile unit or moving to better cover. If the alien kills its target or its target escapes, the alien will resume choosing between overwatch mode and movement mode the following turn.

A good example of why this AI system is an improvement is a UFO assault. In Xenonauts 1 the AI was based around finding optimal tiles to move to based on how good the cover and sight lines were, which is why you'd usually find the aliens crouching behind cover in the middle of the UFO and refusing to move (because they were already in mathematically the "best" position). This means they would rarely check outside the UFO to see if there were any enemies there, or go for a stroll through the interior of the UFO, or really do anything particularly interesting beyond camping the door.

In the new system, the tile outside the door is just one tile on a semi-randomised patrol route. Some of those tiles might be good defensive locations watching over the door, but others might be checking outside the UFO, standing inside small rooms, working on an alien console, etc. A level designer can probably do a better job picking interesting places for aliens to stand than an algorithm can. This means breaching a UFO is likely to be a more interesting experience, and when you're inside a UFO the aliens will patrol around more and so are more likely to surprise you.

Finally, the waypoints allow us to specify the behaviour of the aliens standing on them - e.g. you can set an alien to face a specific direction, or crouch. This means the AI doesn't need "cheat" like it did in the first game, where the units would often turn to face the closest Xenonaut unit (even if they couldn't see it) when attempting to defend a UFO. Because the AI didn't know which doors were the ones the player was most likely to breach through, without this hack the aliens would all be facing random directions when you entered a UFO and wouldn't put up much resistance to your assault.

Problem is, this hack would cause problems with destructible UFOs - even if you blasted a hole in the hull to make a side entrance for your team, the aliens would still be facing towards you. The new system means we can tell the aliens which way they should be facing (i.e. towards the big door to the outside) and that gives you the opportunity to surprise them by taking advantage of destructibility. Rewarding smart play is important, and the new AI system will help us to do that.


Further Changes:
Some of these changes are actually quite significant changes to the way combat and damage works, but for the sake of brevity I'll just give a quick summary of each system.

  • Rotatable Camera: the biggest advantage of a 3D engine is you can now rotate the camera. You might not realise how much you want this now, but trust me - you'll miss it if you go back to X1 afterwards!
  • Alien Weapon Tiers: the aliens aren't using plasma weapons right from the start of the game. They now start using magnetic weapons and begin to deploy energy weapons in the mid-game, and eventually advance to a third tier of even more powerful weapons. This is important because weapon penetration is now relative (see below).
  • Armour HP & Penetration: Armour HP is now a separate pool of hitpoints that are drained before damage is applied to the unit underneath. However, armour resistance and penetration are relative values and if the armour resistance is higher than the weapon penetration, the incoming damage is reduced. If penetration is higher then a portion of the damage penetrates through the armour and damages both the Armour HP and the HP of the unit.
    • In practice this means that the tech progression is a bit more interesting. Power armour like the Predator Exosuit from X1 is totally impervious to low-tier alien weapons, whereas a powerful alien plasma weapon is going to punch straight through Kevlar no matter how much of it you're wearing.
  • Locational Damage: Weapons no longer do a random 50% - 150% of their base damage on hit, but instead the hit is assigned to either the torso, head, right arm, left arm, right leg or left leg. Hitting the torso does normal damage, hitting the head does 150% damage and hitting a limb does 75% damage. In the future we're likely to add locational injuries as a result of this.
  • Symmetrical Vision: the line of sight algorithm in the first Xenonauts had some awkward spots where it was possible for units to fire around corners without the target being able to fire back (this was because of the way walls worked). This won't happen in X2; vision and shooting is entirely symmetrical.
  • Body Size: as some aliens are bigger or smaller than others, we've added a simple body size modifier to each unit that affects how easy they are to hit - e.g. a particularly big and tough Sebillian might be 30% easier to hit than normal. Just a small thing that helps differentiate different alien units from each other.
  • Alien Night Abilities: the aliens were all pretty interchangeable at night in X1, which in retrospect was a wasted opportunity. It would be more interesting if some aliens are particularly strong at night and others were weaker. Perhaps the Psyons (formerly Caesans) would be a really tough prospect at night because they have perfect night vision and their psionics had more chance of success in darkness. Whereas fighting the Wraiths at night might actually give you an advantage - they've got big glowing bulbs on their head, so we could literally make them glow in the dark.


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I understand why you're leaving the boxy UFOs behind, but if at all possible, please keep the assets in the game files - they could be great for modding and mapping.

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Seems like a good update.

On 5/20/2020 at 5:48 PM, Chris said:

Locational Damage: Weapons no longer do a random 50% - 150% of their base damage on hit, but instead the hit is assigned to either the torso, head, right arm, left arm, right leg or left leg. Hitting the torso does normal damage, hitting the head does 150% damage and hitting a limb does 75% damage. In the future we're likely to add locational injuries as a result of this.

I dont really see why the randomised damage has to be abandonded with this system. As a suggestion you could randomise body part damage too.

torso: 75% - 125%
head: 125% - 175%
limb: 50% - 100%


For the AI thing it sounds super exploitable to just stand still and overwatch until all aliens ran into your fly trap.

Edited by Charon

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Here I wanna say something as an Beta-Tester too.

1. The Ground-Battles are fair and hard. Esp. in the first Monthes you have to watch for your Soldiers not to die, because your Safty Suit is only optimised for Human Weapons. The heavy Cevlar-West helps a little bit, but Cover is still your best Friend.

2. The Missions have to be more. The new testet Missions (which are atm interim solutions) are nice. They were be nicer if you can play it Manually.

3. UFO-Upcommings are good and the Crash-Site-Missions don´t need more. To less Crash-Site-Missions are also not good. A middleway have to be found. Maybe you can also give Crash-Site-Missions you can´t do atm to the States. Then you will only get 50 % of the outcome from the UFO and Aliens.

4. Haven´t played Base-Defense and attack on Alien-Bases yet, so there I coulnd´t give a statement to it.

5. The exisitng UFO´s are breachable, which are nice. But the Walls are to weak and an Vehicle can open a second entry without any damage on it. C-4 Explosives for the Soldiers are unnessecary, which is realy sad.

6. The existing Armor-System isn´t good, because the Cevlar-West / Warden-Vest dosen´t give enough protection for it´s weight. So I´m exited  to see the new Armor and HP-System in Beta 13.

7. The new Variations from the Aliens are cool. The Races have more Variants, which gives the Interrogation more possibilitys. So you need Technicans for more technical knowledge, Soldiers for better Weapons and so on.

8. The AI Improvement is much better in the Beta then Expected. Everything Chris said already I can agree to the Predecessor X1. More Improvements were good and necessary for the final Base-Version for X2.

The other further Chances get a Test in Beta 13, 14 and there we will see what needs bugfixing, reworks and so on, before they get final in Early-Access and final Base-Version.

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I guess I might be a little too late to the party to make feature suggestions at this stage, but anyway: what I found added even more tactical options to Jagged Alliance 2 (not sure if this existed in the vanilla game or was added by a fan patch, but I think it was part of the base game) and would perfectly work in Xenonauts too are those mechanics:

  • a third stance besides standing and crouched - proned (better protection and aim, extra movement points spent)
  • the possibility to move while keeping the stance (i.e. crouched and proned, which costs more movement points but preserves the benefits of the stance)
  • the possibility to move backwards/sidewards while keeping the same facing

Maybe those things could be something for later. :o

Edited by Tronski

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Ideas and constructive Critics are nice to have, which makes the Game better and more interessting.

There will come more from the Devs (esp. Missions, Maps and such) and your Ideas are very good. I thougt too, that the Hit Chance get higher with Crounched and Proned (like in Biathlon which have Proned Shooting).

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