Encounters
Table of contents
Encounter formation and condition
Mechanics
When an encounter is triggered the game uses RNG1 to determine both the monster formation and the encounter condition (Normal, Ambush or Preemptive Strike).
If the encounter triggered has a forced formation (for example a boss) RNG is only advanced to determine the encounter condition. Most bosses and some random encounters force a specific encounter condition (usually Normal), in that case RNG is still advanced but the result is not used.
Triggering an encounter advances damage RNG to determine ICVs, you can find more details here.
Formula
The game determines the formation first:
formation rng = rng value MOD # of formations in the zone
The formation used will be the Nth formation in the zone, where N is Formation RNG.
The encounter condition is determined as follows:
condition rng = rng value AND 255
if a character in the active party has an initiative weapon equipped:
condition rng -= 33
if condition rng < 32 the condition is preemptive
else if condition rng < 223 the condition is normal
else the condition is ambush
if the encounter has a forced condition use that instead
Notes
Since forced encounters use only 1 RNG value and random encounters use 2 RNG values it is possible to change the formations in the future random encounters: by getting an additional forced encounter (thus advancing RNG1 once) the values that would have been used to determine encounter formation now will be used to determine encounter condition and the one used for encounter condition now will determine the formation for the next encounter; it’s possible to get an additional forced encounter by interacting with the Lord Ochu in Kilika Woods, the Guados chasing you in Macalania Temple, the Sandragoras in Sanubia Desert (West) or by starting a simulation encounter.
Encounter checks
Mechanics
Every 10 units of movement in an hostile zone an encounter check is generated, RNG0 is advanced and the RNG value is checked against a check counter determining if an encounter is triggered or not; when an encounter is triggered or the zone changes both the distance counter and the check counter are reset to 0.
Every hostile zone has a Danger Value that determines the Grace Period, how many encounter checks to skip when entering the zone and after every encounter, and the Threat Modifier, used to determine how fast a counter that is compared to the RNG Value increases. The bigger the Danger Value is the longer the Grace Period is gonna be and the slower is the counter is gonna increase.
Formula
The Grace Period and Threat Modifier are calculated as follows:
grace period = danger value // 2
threat modifier = danger value * 4
At every encounter check the game performs the following calculations:
check rng = rng value AND 255
check value = (check counter * 256) // threat modifier
if check rng < check value then trigger an encounter and reset the counters
else increase the check counter by 1
Notes
When trying to force random encounters it’s beneficial to move as fast as possible by not doing sharp turns since movement speed is lowered during the turn animation.
While it is technically possible to plan a steproute for a specific seed to artificially lower encounter rate it’s not easy to exactly figure out how many times RNG0 has been advanced and given how movement works in FFX it’s not easy to have perfectly consistent movement either; it is possible however to know somewhat accurately how many encounters there will be in each screen for a specific seed by just playing it through a handful of times.