They Are Billions 800% Guide

I recently beat 800% (the maximum level of difficulty) and wanted to share what I learned for others who might attempt the same goal. It took me 450 hours of play total to unlock all 4 maps and beat the game at this difficulty (this is probably above average; I know another player that took 300 hours). There’s already a great guide on Google Docs They Are Billions Ultimate Guide and others on Fandom that this overlaps with. I include some strategies not mentioned there.

Playing at 800% is a completely different game than lower percentages. The techniques used are unique to this level and you’ll likely have to unlearn what you did in earlier games.

Map Selection

The first new concept is map selection, also known as “rolling” for a map. Because the Desolated Wasteland has so few resources, some of the maps the game will randomly generate are probably impossible to beat. I would re-roll over a dozen times per gaming session, sometimes spending 30 minutes to find a good map. My criteria was, in this order:

  1. Initial food >=9 and sawmill >=10
  2. Food (for farms): both amount and proximity to the command center
  3. Terrain: chokes, protection, and entrances
  4. Building space
  5. Resources: stone, wood, iron

After the sawmill check, I found the single biggest determinate of a successful game was a large green patch for at least 4-5 farms each gathering 30+ food. If you don’t have this near your command center, your initial economy is capped and then you must use units to expand for more food. Expanding is extremely difficult early on due to the increased noise sensitivity of the zombies, because even strong groups of units can quickly become overrun.

The ideal terrain is one that has as few entrances as possible, but still with enough space to build lots of housing. I define an entrance as a place that you could have a single archer guard, and block zombies from reaching your buildings. A choke is a narrow entrance. Protection means large chunks of terrain that act like free walls.

Put down a food >9 building and then 7 tents to get first mayor right away. The very best mayor is farm technology, the worst is wood stakes. If you’re lucky with fallen resources on the map, you might be able to build a Wood Workshop next (needs 40 wood) otherwise build sawmill. After that, order depends on the map. Put a quary on stone before day 5 so it has time for building soliders center, market, and warehouse (in that order) later.


800% involves another new behavior from previous difficulty levels, advanced troop movement. It’s important to level up your initial rangers to vet status, so that they can more productively clear and defend against runner zombies by themselves. This means right away (during day 1) you should have them start clearing zombies.

Think of each ranger as having a timer associated with it. After sending a ranger to attack-move into a group of zombies, set your mental timer for that ranger to about 15 seconds before you need to check on it again. You can check on it a number of ways: moving the view, looking at the minimap, or zooming out enough to see them all at once. But you need to develop the habit of checking on each one regularly.

For waves before 800%, you’re probably used to setting up walls and putting your troops behind them to defend. At 800% the sound of zombies beating on walls and structures collapsing will attract too many more zombies so you can’t do this. What’s known as “kiting” is essential. This means moving a unit, a ranger because of their speed, around in a circle or kite-like pattern, which will in-turn cause zombies to do the same, so that other units or your ballistas will have more time to shoot at the zombies. You need to kite for the Day 11 and Day 19 waves, and it can be helpful on Day 26 and 35 waves also depending on how strong your defenses are.

In the early game, "ballista pulls" are important. Day 26 and earlier, place a ballista with just 4-5 infected at the very edge of it's range. Once it's built, use a ranger to run around and create noise near the ballista. The first time, make sure to attract ("pull") <5 runner infected. After than, perform at least 4-5 more pulls on each new ballista you place. This will help with both future expansion, and for waves. If a wave comes towards that ballista in the future, your space for kiting will be more free. In mid-game, ballistas can be placed after groups of snipers have cleared areas.

The workhorses of 800% overall are an initial group of 10+ rangers, two 25+ packs of snipers to clear, and 30+ thanatos to defend waves. You can keep the thanatos in your base.

What To Do at Any Given Moment

At any given point in the game, there’s basically 4 types of activity you might need to do:

  1. Economy
  2. Expansion
  3. Technology
  4. Train

You can remember the acronym “EETT”. 

Economy: the most important resource is gold production per period. Gold is the lifeblood of the game. If you don’t hit certain gold production levels by certain times, you won’t be able to beat later waves or the final wave because your defense won’t be strong enough.

Expansion: using your troops to clear zombies and expanding the colony.

Technology: since researching takes time and 800% only gives you 80 days, it’s important to research things “on schedule”. For example, if you don’t research bank or foundary in between day 30 and 40, your colony will fall to some of the larger later waves because you’ll need thanatos for defense.

Train: unlike lower difficulties levels that give you 100+ days to defend and plenty of time to build up and train troops for your armies, 800% requires building armies very quickly. This means multiple soldiers centers. I used 2 with 1 engineering center (the advanced soldiers center) although some players use 3 and 2 respectively.

If you wanted to be thorough about these steps, you could pause the game roughly every 8 hours (also known as “every tick”) and go through this list of these 4 types of activities to see if anything needs to be done.


The most difficult aspect of 800% is the race against the clock. Preparing to defend against a final wave in 80 days (the final wave actually shows up on day 73) means every in-game hour must be spent productively. Here are some numbers for what you should be achieving by when:

Day 11: researched farms, cottages, ballistas, market (roughly that order). More than +450 gold production.

Day 19: make sure the colony is defended with ballistas due to the random swarms after this day. >+550 gold production.

Day 30: >+700 gold production. You should have built or be building your Stone Workshop because by…

Day 35 you’ll want stone walls to defend this incoming wave

Day 40: build the foundary, and then engineering center asap after. If your economy isn’t strong enough by this point, to build these, it will be difficult to win.

Day 52: you need >3 thanatos to defened against this, and then >10 for later waves, and you should be hitting

Day 64: no more mini-waves at this point; your gold should be >+3000

The Final Wave

Lot's of snipers and thanatos. You can beat it with 100 snipers but it's easier with 200. Use 40 thanatos and keep them alive by having them fall back behind walls if their areas get overrun.

I recommend pausing and analyzing the map for choke points. Decide which will need to be most heavily defended, considering each of the cardinal directions (north/east/south/west) and put two layers of double stone walls along with ballistas and executors. Distribute your snipers, and thanatos. Fewer, well-defended chokes work better than many weakly defended ones. While the final wave is in progress, expect to need to pause and build more walls (with gates) and move units around; don’t expect to setup all your defenses beforehand and then sit back and watch what happens.  Also, you’ll need to demolish buildings, particularly farms and housing buildings as those can significantly contribute to the size of inbound infected, if they're overrun.

Since you can build walls without energy, it’s safe to demolish mills and power plants. Demolish housing as zombies reach those parts of your colony, so that they don’t add to the infected and so that you recover their resources to build more walls. If enough days go by with negative gold, units will desert, but this takes 3-4 days and happens gradually and hopefully you’re most of the way finished with the final wave by then.


Here’s a few common problems players have at 800%:

Stray zombie wanders into your colony causing an infection to spread: this happens to even the best players (watch a bit of AznElite123 on YouTube or Twitch). So first, live with the fact that this will occasionally happen. The best way to combat this problem if it happens to you repeatedly, is roll for a map with as few entrances as possible. If your map has only 3 entrances (as defined above) it will cut down on the chances of this happening. Another way to combat this, is after you have gotten your initial 4 rangers to vet status set them to patrol entrances. Then, only clear further zombies with newly trained rangers. Large entrances to your colonies might need two patrolling rangers. Set them up to each patrol a section of the entrance, as opposed to both going the length of the entrance.

Too much ballista aggro (inbound flood of zombies) on newly built ballistas: as you expand after the wave on day 19, sometimes a newly placed ballista will quickly attract dozens of zombies and both get infested and cause an invasion in your colony. The best thing to combat this is very careful placement of the ballista. The key is that no more than 4-5 zombies should be within the very outer ranges of the new ballista. There should be no zombies at all closer than half the distance from the ballista to its outer range. You should also wall around the sides of half the ballista at the same time you build it. If you don’t have enough resources to build the ballista plus walls, don’t build it yet.

Units overrun during expansion: in the early or mid game, you send out units but they get overrun and you either take losses or lose progress and time clearing. First, don't worry if you're not clearing much before day 26. Second, do ballista pulls to clear up areas immediately around your base. This will help units start to expand. Third, clear either with >5 rangers and lots of micromanagement (retreat to ballistas at first sight of trouble) or with large 25+ groups of snipers. Finally, develop a feel for nearby villages of doom (infected cities). You'll be able to tell by a large influx in the rate of infected, with special infected (spitters, harpies) mixed in. Retreat to ballistas immediately and clear in a different direction until strong enough - and even then, proceed very slowly.

Overrun by early (Day 11 through Day 26) waves: you need to kite (explained above). If it’s a common problem for you, add a criteria to your map selection for “kiting space” and make sure to build ballistas such that you have plenty of free space, without attacking more runner zombies, to run around in circles. 

Overrun by mid (Day 35 through Day 46) waves: you need stone walls, 2-3 ballistas, and a 20+ pack of snipers. Also, take into account the terrain and ideally build at chokes (narrow entrances to your colony). Keep a post-it note near your computer with wave timings, and bring your group of snipers back into position in time to defend. Some people use shocking towers. I don't due to their high energy cost, limited range (i.e. need to be paired with ballistas to combat spitter zombies, which can sit out of shocking tower range and take it down), and need to more carefully place.

Overrun by later (Day 52 through Day 65) waves: you need a 20+ sniper pack, >2 thanatos and 3 ballistas. If you have enough thanatos (>8) you don’t even need snipers - you can leave the snipers out around the map clearing.

Too weak economy (i.e. can’t build engineering center on time - see Timeline): This is one of the toughest problems to troubleshoot, as it involves so many factors to have a strong economy. Make sure to build dense, correctly laid out cities (see the housing layout guides on Fandom). Use "Center Rows". Track your economy progress against the gold production guidelines I give above to isolate where you’re falling behind. You’ll need 2.5 cities by the final wave, where the first two cities are mostly stone houses with some cottages. 800% (as opposed to other difficulty levels) was the only time playing the game where I found workers sometimes in short supply. Any of the housing types (tent/cottage/house) provide workers at the same rate per food, so build whatever you have resources for. Tents are most energy efficient.

I recommend 800% to anyone who has beat the lower difficulty levels and wants to enjoy the game further. I hope you’ve found this guide helpful.


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by Jonathan Berger
San Francisco Updated: April 30, 2019