Spawning

tl;dr

• Mob spawn rate is very slowly increased until a mob is spawned, to counteract RNG
• Only one mob can spawn on a frame; mob 1 gets priority over mob 2 gets priority over mob 3
• Mobs have a 0.8% chance to spawn with 1.5x HP and give 3x experience
• Bosses only process every third arrow hit detection — it can take up to 3 frames for an arrow to damage a boss
• After a boss is killed, the gradual increase of the spawn rate is multiplied by 2.2

First, when the mission is started, these variables are initialized:

spawndrought = 0; 
spawncount = 0.05;

spawndrought is a value for RNG smoothing, which increases by spawncount every frame until a mob is spawned (except on the ascension mission).
spawncount generally stays the same, except on boss missions: it gets multiplied by 2.2 (final value of 0.11) when the boss is killed.

function monsterdeath() {
    if (_local1.bossres != undefined) { 
        spawncount = spawncount * 2.2; 
    } 
    // ... 
}

As well, the mob data from slot 1, 2, and 3 is stored into spawna, spawnb, and spawnc like this (see [Mission Data](Mission Data)):

// mid is the mission id, starting with 1 at Green Snails Only 
spawna.odds = levellist[("m" + mid) + "o1"]; //spawn rate 
spawna.speed = levellist[("m" + mid) + "s1"]; //speed 
spawna.xp = levellist[("m" + mid) + "x1"]; //EXP 
spawna.hp = levellist[("m" + mid) + "h1"]; //HP 
spawna.kb = levellist[("m" + mid) + "k1"]; //knockback 
spawna.linkid = levellist[("m" + mid) + "n1"]; //sprite image tag 
spawna.growth = levellist[("m" + mid) + "g1"]; //size increase of boss sprite 
spawna.ystart = levellist[("m" + mid) + "y1"]; //y-position of boss 
spawna.bossname = levellist[("m" + mid) + "b1"]; //display name of boss 
if (levellist[("m" + mid) + "t1"] != undefined) { //the colour effect 
    spawna.fx = levellist[("m" + mid) + "t1"]; 
} else {
    spawna.fx = 1; 
} 
/* repeat for spawnb, spawnc (without the boss attributes)... */

For the ascendance missions, the hp and kb scale with the number of ascents.

spawna.hp = Math.round(levellist.mX1h1 * (1 + (ascends / 8))); //ascendant 
spawna.kb = levellist.mX1k1; 
spawnb.hp = Math.round(levellist.mX1h2 * (1 + (ascends / 7))); //red snail 
spawnb.kb = Math.round(levellist.mX1k2 * (1 + (ascends / 5))); 
spawnc.hp = Math.round(levellist.mX1h3 * (1 + (ascends / 6))); //alishar 
spawnc.kb = Math.round(levellist.mX1k3 * (1 + (ascends / 5)));

Now the spawning code initiates. First, the boss is spawned if there is one:

if (spawna.odds == 13370) { 
    /* ... create mob (named "bossmob" here) with the attributes {
        _x:646, _y:spawna.ystart, hpx:1, bossres:5, dieframes:20, 
        kb:spawna.kb, xvel:spawna.speed, experience:spawna.xp, 
        hp:spawna.hp, fx:spawna.fx } */
    if (missionid == "X1") { //current mission is the ascendance test 
        bossmob._x = 400; // move ascendant to the center of the screen 
    } 
    bossmob._xscale = spawna.growth; //resize the boss sprite 
    bossmob._yscale = spawna.growth; 
    hpbar_mc.gotoAndStop(2); //show hp bar 
    hpbar_mc.bossname_txt.text = spawna.bossname; 
    this.bossfight = true; 
}

The boss (and all mobs) are spawned with some attributes: _x and _y are the x and y position of the mob on the screen, hpx is the HP multiplier (used in score calculation — see Scoring), dieframes is unused(?), xvel is the speed of the mob (in pixels/frame), and experience, hp, fx should be obvious. bossres (boss resistance?) seems to be a damage spreadout feature, which makes the boss gradually absorb arrows rather than all at once.

for ([each arrow on screen]) { 
    if ([arrow should hit this mob]) { 
        if (bossres == undefined) { 
            _root.assassin = false; //non-boss hit, don't award the Assassin badge
        } 
        if (bossres > 1) { 
            bossres--; 
        } else { 
            if (bossres != undefined) { 
                bossres = 3; 
            } 
            /* [... perform arrow calculations] */
        }
    }
}

bossres is decremented once per touching arrow per frame, and is reset to 3 when a hit check is calculated. This makes the boss only process every 1 in 3 arrow hit detections — it can take up to 3 frames for an arrow to inflict damage on a boss. You might notice this effect on smaller bosses, ex. shooting a full Hurricane at Athena Pierce will cause some arrows to pass through her.

Now the main spawning code is run on every frame:

if ([current mission is not ascension]) { 
    spawndrought = spawndrought + spawncount; 
} 
chaos = Math.random() * 1000; //Math.random() returns a number 0 <= n < 1 
spawnplz = spawna.odds - spawndrought; 
if (chaos >= spawnplz) { 
    spawndrought = 0; 
    /* ... create mob (named "mob" here) with the attributes {
        _x:668, _y:235, hpx:1, dieframes:20, kb:spawna.kb, 
        xvel:spawna.speed, experience:spawna.xp, 
        hp:spawna.hp, fx:spawna.fx } */ 
    if ((Math.random() > 0.992) && (spawna.fx == 1)) { // randomly make mob stronger 
        mob.experience = mob.experience * 3; 
        mob.speed = mob.speed * 1.6; //doesn't work as intended -- should've been named xvel 
        mob.hp = mob.hp * 1.5; 
        mob.hpx = mob.hpx * 1.5; 
    } 
} else { 
    spawnplz = spawnb.odds - (2 * this.spawndrought); 
    if (chaos >= spawnplz) { 
        /* ... do the same as above, but with spawnb, and spawning at _x=666 */ 
    } else { 
        spawnplz = spawnc.odds - (3 * this.spawndrought); 
        if (chaos >= spawnplz) { 
            /* ... do the same as above, but with spawnc, and spawning at _x=666 */ 
        } 
    } 
}

The code checks the spawn conditions of each mob sequentially, mob A, then B, then C. Once a mob is spawned, no further checks are done (only one mob spawns per frame). The check is done by checking if chaos, a random number between 0 and 1000, generated once at the start, is greater than spawnplz, which is the spawn odds minus spawndrought (2x and 3x spawndrought for mob B and mob C). If chaos >= spawnplz in any of these checks, then that mob is spawned.

Mobs have a 0.8% chance to have 1.5 times the normal HP and give 3 times the EXP, if it has no colour transformation (= all mobs except in the radioactive missions and the ascension stage). Note that hpx is changed with the hp. The mob’s speed is supposed to change as well, but the speed attribute is modified instead of xvel — whoops.

spawndrought doesn’t increase very fast, at a rate of 0.05 each frame, or 1 every 20 frames. Hunterstory runs at 30 FPS, so it takes 0.666 seconds to increase the spawn chance by 0.1%, or 6.666 seconds to increase it by 1%. These numbers are roughly doubled in a boss mission, after the boss is killed. spawndrought is always at least spawncount during the checks, since it’s incremented before the checks are done.

Notice that bosses or empty mobs have their spawn rates way higher than the maximum value for chaos, so they won’t spawn under normal conditions. Theoretically, spawndrought could increase enough to lower spawnplz within the range of chaos, but this needs spawndrought to be greater than 1000, and at that point the value of spawnplz for any normal mob would be below 0 and its check would always pass. Since there’s no missions without a normal mob, bosses can’t ever spawn naturally. :(