I first discovered They are Billions a few months back, but even then I was pleasantly surprised by a few things: the level of polish, especially for a game still in development; the easy-to-understand yet complex-to-execute rules that directed the building of your colony; and the difficulty. There may be billions, but all it takes is one misplaced zombie to turn most of a colony into a screaming horde of flesh-eating maniacs.
I got hooked quickly and lost countless hours trying to come up with the best strategy to defend my base. I lost many rangers, soldiers, colonies, and a whole lot of sleep trying to fend off the hordes of ravenous undead. It was a rollercoaster of emotions, from excitement at the sight of the final wave to frustration when my three-hour-old colony got crushed, and triumph as I finally beat the first map.
It's easy to become frustrated and feel like They Are Billions' survival mode is impossible to beat unless you're a StarCraft veteran or some insane mutant keyboard ninja, but I’m here to give you a few tips and points on how yours truly managed to defeat it.
Use the pause button to think
Don't worry about destroying your spacebar as you frantically pause and plan your next move. Use this time to check the calendar to know how much time you have left before the next wave. Never leave a portion of your base unattended, use the patrol move (the shortcut is P) on your units so they cover the most area, and to be sure no zombie can pass through your defenses.
Slower zombies roam the interior of the map, so they're easier to catch with your speedy Rangers. But don’t forget that special infected roam the northern and southern side of the map. If possible, expand to the east or west first to avoid activating them too early.
Expand to focus on generating gold
You're going to need billions to defeat Billions. Gold is used for everything: units; research; buildings; defenses. You'll need not just a big bank (through Warehouses, which store gold and resources), but a strong income rate to allow you to recover quickly.
Treat land as gold. With more land you will have more food and therefore be able to build more houses. You need to expand early. If your Rangers spot some free stone on the map, save it for a Soldier Center—more units means more area you can own and protect. As far as research goes, if you don’t have good food revenue you should aim for Farms first (if your first mayor offers you Farm tech, elect them immediately), otherwise aim for Cottages first.
The very first thing you want to build is either a Fisherman's Cottage or a Hunter's Lodge, depending on your starting position. You'll need the food. Follow that by dropping seven Tents to get your worker numbers up, and also so you hit the first mayoral election as soon as possible. Make sure to leave room on the green grass for Farms.
The Market and Bank buildings should literally be at the center of your housing so plan for that from the start. The Bank increases the gold output of surrounding buildings while the Market reduces the food cost of anything in its radius, and you should build a massive, dense housing district around them. You can only have three such districts so plan carefully on where you will put them for maximum efficiency. Markets also let you sell excess resources and though they'll do so automatically, it's more efficient to do so yourself.
Don’t build advanced buildings if you can expand and find resources elsewhere. Most of the time their steep upkeep cost will only hurt your economy.
Rangers early, Thanatos late
Tiptoe in the early game but be ready to rumble in the late game. Zombies look so inoffensive with their low pool of HP and slow shuffling, right? Wrong! They are lethal death machines that will swarm you. Some of them can run, some of them can hop over walls, some even spit splash-damaging acid. In the early game you don’t want them banging at your door and so you want to make as little noise as possible. Thankfully, humanity have given you the perfect tool for this job: the Ranger. Armed with a bow and arrow they deal with the infected threat as silently as possible. The Sniper is also a viable option, but they generate much more noise, and will eventually attract lots of undead if they're firing often. Be especially careful around a Village of Doom—the ghastly haunted houses that contain a large but finite amount of undead—as an early army will not prevail.
Once you've built up a reliable defense, put together a mobile fighting force for clearing the map. I like a mixture of Rangers, Snipers, and Thanatos, and a Titan or two if you're economically booming. You can hit the C key to command these units to 'chase,' or seek and destroy any and all zombies on the map, though you'll still want to micromanage your forces, as they won't do much to arrange themselves intelligently. It's important to clear as much of the map as you safely can before the final wave, where any spare undead will join the finale. Map hygiene might make all the difference.
Layer your defenses
Never neglect your defenses. You think that this massive wall protected by a plethora of Executors and Ballistas will be enough? Think again. Assume the worst, and focus on reinforcing your weakest points first. Always layer your base and use chokepoints to organize those layers. By the final wave, zombies coming from any direction should encounter at the very least three layers of stone walls protected by Executors.
Executors are your best pals. Build them everywhere. Don’t get tempted by the Shocking Tower, which costs tons of energy and won't give you the DPS you need in the endgame. Consider spike traps as a luxury, too: they're resource-intensive and not durable enough to be of much use. Ballistas are all good in the early game and have the advantage of being upgradable to Executors. But in the end, Executors are your BFFs, paired with layers of stone wall. Build them everywhere, pause the game when there’s a breach, and delay the horde with layers after layers of walls. Only then will you prevail.