The phenomenal world of Horizon Zero Dawn is filled with lots of secrets and nuisances for players to discover during their run. As players make their way through the narrative, the enemies they encounter will get progressively more difficult and not simply because newer machine types are harder to bring down. In fact, Horizon Zero Dawn features a unique, subtle mechanic which has machines "evolving" and adapting based on player behavior.
Machines are the primary enemies the game's main character, Aloy, will face off against. Hunting these machines lends important crafting materials and quest items that are necessary to progress through Horizon Zero Dawn's story and upgrade Aloy's arsenal. Players will need to familiarize themselves with each machine's abilities and behavior if they want to survive. Each unique machine has their own set of weak points which, if hit, can greatly aid in bringing it down. However, the more the player hunts a particular "species" of machine, the more they "evolve" to protect themselves against attack.
In this aspect, the designs of the machines are never truly fixed or constant throughout the entirety of the game. As the player hunts more and more machines, they will incrementally "evolve" to protect themselves with the addition of new armor plating. Each machine type has their own number of kills required before they are able to "evolve". Once an evolution occurs, players will begin to encounter more heavily armored variants of the original machine. When the evolution occurs is entirely dependent upon the player, meaning some players will achieve an "evolution" sooner than others.
Horizon Zero Dawn: Machines Evolve And Adapt As They're Hunted
The more dangerous and rare machines "evolve" faster than the common heard based "species". A the Corruptor and the Deathbringer are unaffected and will remain the same throughout the game.
Additionally, machines will also adapt and become "smarter" based upon how Aloy approaches them. If players often take the high ground and sneakily snipe out their target machines, the machine type will begin to avoid getting near high ledges. This change forces players to come down and kill the machine directly rather than taking a more long-range approach. A similar adaptation can occur with traps. Should players prefer to use traps to ensnare their target, machines will start to become suspicious and avoid traps entirely. They will likely stop right in front of the trap and look around before walking away from the trap. These types of adaptations means that players cannot depend on one strategy throughout the entirety of their play-through. So don't expect to be able to one-shot a Watcher into the late game.
These clever and subtle changes keep the machines in Horizon Zero Dawn feeling alive and real. As the player learns, so do the machines, forcing the player to constantly problem solve and stay alert if they want to succeed. Even a little bit of additional armor over a Sawtooth's canisters can suddenly up the difficulty to a whole new level. While many players will likely not notice these "evolutions" and adaptations directly, the additional level of challenge that comes with them is sure to garner a few strategy changes.