Why would anyone become a multiplier? It's simple really. You know how great having a body is, compared to not having one? Well just imagine how great it is to have two bodies. Now imagine - that's just the start of what I can do.
- Valruaa Golgandi, one of the few who has been seen in two places at once

A multiplier is someone who's decided the limitations of only being in one place at one time were just too much for them to bear. The multiplier can split into two, four, 16, 1000, even 100,000 smaller versions of itself as it desires, with all the additional maneuverability and freedom that elicits.

Almost anyone can become a multiplier (even gnomes and halfling may be able to meet the requirements, if under the effects of a permanency'd enlarge person), though the class appeals mostly to those characters who neither excel nor specialize in ordinary or magical combat. Specifically, evasive/survivalist characters (such as the scout, monk, or rogue) are more likely to find utility in the abilities the multiplier class offerse, though even a spellcaster or barbarian can gain benefits from the multiplier's abilities (provided that spellcaster is willing to lose out on some spellcasting levels, that is.)

Size: Medium or larger
Feats: Endurance, Diehard
Skills: Escape Artist 8 ranks

Class Skills
The multiplier's class skills (and the key ability for each skill) are: Balance (Dex), Climb (Str), Concentration (Con), Craft (Int), Disable Device (Int), Escape Artist (Dex), Hide (Dex), Move silently (Dex), Sleight of Hand (Dex), Survival (Wis), Swim (Str), Tumble (Dex)
Skills Points at Each Level: 4 + Int

Hit Dice: d8

Level Base Attack Bonus Fort Save Ref Save Will Save Special
Lesser amorphous traits
Many bodies, one mind; split (max bodies x2)
Split (max bodies x4)
Flash split, swarm form (Tiny)
Split (max bodies x8), swarm combatant
Swarm form (Diminutive)
Armed swarm, split (max bodies x16), swarm split
Swarm form (Fine)
Split (max bodies x32), swarm form (gaseous),

Weapon Proficiencies: Multipliers do not gain any weapon or armor proficiencies.

Lesser Amorphous Traits (Ex): At 1st level, a multiplier's body is altered in the most basic ways necessary to make use of his later abilities. He is immune to critical hits as well as polymorph effects and any other effect that would alter his form. He may choose to voluntarily allow a shapechanging effect to affect him.

Split (Su): Beginning at 2nd level, the multiplier gains his first body-duplicating ability, reminiscent of the ability some oozes possess. When damaged by an attack by a piercing or slashing weapon, the multiplier may, as a free action taken out of turn, immediately split into two smaller copies of himself occupying adjacent spaces. Each copy is one size category smaller than the original (adjust ability scores as described in the Monster Manual), possesses 1/2 the current hit points of the multiplier's original body, and has duplicates of all his items, resized appropriately. Further piercing or slashing attacks deal damage normally to these split-copies. If the total hit points of all the multiplier's bodies becomes zero or below, or equals or exceeds the multiplier's normal maximum hit points plus the total of all bonus hp granted by Strength in Numbers (see below), all bodies reconverge into one of the character's original size immediately after the damage is resolved; the newly-converged body is formed in any space occupied by one of the copies, at the multiplier's discretion.
At 3rd level, a multiplier who has split into two bodies can be split one size category further. Thus, a human multiplier attacked in one round with a longsword splits into two Small humans; if attacked once more, he will further split into two Tiny humans, in addition to the one remaining Small human (which itself could be split into two Tiny ones). At 5th level, he can divide into a number of bodies up to three sizes smaller than his normal size, at 7th level to four sizes smaller, and at 9th level to five size categories smaller (in all cases, the minimum size a multiplier can split into is Fine; additional size category reductions beyond this stage do nothing, and are provided only for very large characters who gain levels in this class, such as a Giant).
Although each body possesses duplicates of the original's possessions, certain items may function differently. Each item with a limited number of uses (such as a use-activated item useable 3/day, or wands or other charged items), determines its remaining uses from a single, shared pool. Mundane, expendable items (such as arrows, sling stones, or pints of lamp oil) are duplicated, but magical expendable items (such as enchanted arrows, potions, scrolls, or flasks of alchemist's fire) are not; all bodies have access to these items, but if one uses it, it disappears from all other bodies' inventories as well.

Many Bodies, One Mind (Ex): Though the multiplier's Split ability creates multiple bodies, these bodies share one mind. No single body is considered surprised, flat-footed, or flanked unless all of them are. All bodies are aware of the same dangers; the multiplier perceives his environment through all bodies simultaneously. In addition, as a multi-bodied single-consciousness being, the multiplier still cannot cast more spells in a given round than he is normally allowed (normally, up to one spell and one quickened spell). This includes the use of spell-completion and spell-trigger magic items. However, multiplier casters do have an advantage: though the components of spellcasting are not affected by any of the multiplier's class features, he can divide the origin of the components and the spell itself between any of the bodies he controls; thus, one body could perform the somatic components, a second could speak the vocal components, a third could manipulate the material component, and a fourth body could be considered the source of the spell for purposes of determining range, cover, etc. Any spells the multiplier casts while split with a range of Personal or a target of You affect only the body designated as the source of the spell; spells with a range of touch can be delivered by any of the bodies (thus allowing spells which can affect multiple touched creatures to do so in a single round, rather than over the course of several rounds of touching).

Strength in Numbers (Ex): Beginning at 3rd level, when a multiplier splits into smaller copies of itself, each copy receives a number of temporary hp equal to the multiplier's HD. If the multiplier splits again, each newly-split copy gains additional temporary hit points in this way. This ability allows the multiplier to survive even in very tiny forms.

Flash Split (Su): A 4th-level multiplier can take a standard action to voluntarily split, as though having taken piercing or slashing damage. Splitting into further smaller bodies requires additional standard actions on the part of the individual body that is to split. Flash split does not provoke attacks of opportunity.

Swarm Form (Su): Beginning at 4th level, the multiplier can voluntarily discorporate himself into an organized group of much smaller bodies. One per encounter (and no more than 5/day), as a full-round action which provokes attacks of opportunity, the multiplier can become a swarm of Tiny copies of himself. His size becomes Tiny, space becomes 10ft, reach becomes 0ft; he gains the swarm subtype, and loses his armor and shield bonuses to AC, as well as all natural and weapon attack options (including all use-activated items, including those activated with purely mental actions or with command word activation; but see below), instead gaining a swarm attack dealing damage based on his total HD (see table).
Multiplier HD Swarm Attack
1-5HD 1d6
6-10HD 2d6
11-15HD 3d6
16-20HD 4d6
21+HD 5d6
In addition, the multiplier gains the following ability while in swarm form: Distraction (Ex): Any living creature vulnerable to a swarm’s damage that begins its turn with a swarm in its square is nauseated for 1 round; a Fortitude save (DC 10 + multiplier level + multiplier's Dex modifier) negates the effect. Spellcasting or concentrating on spells within the area of a swarm requires a Concentration check (DC 20 + spell level). Using skills that involve patience and concentration requires a DC 20 Concentration check.[/TD]

A multiplier in swarm form whose health is reduced to 0 or below or who is otherwise rendered unconscious reconverges into his original form, as described in the Split ability. Otherwise, a multiplier can remain in swarm form for a maximum of 1 minute per multiplier level, or revert to his normal form as a standard action (which also provokes attacks of opportunity).
At 6th level, the multiplier can assume the form of a swarm of Diminutive versions of himself, and a swarm of Fine copies at 8th level.
Gaseous Swarm: At 9th level, the multiplier can assume the form of a swarm of creatures so miniscule they are imperceptible as individuals to all but the most trained of the naked eyes. This form uses the statistics for the swarm of Fine creatures, but with a +16 size modifier to AC instead of +8. In this gaseous swarm form, the multiplier gains a fly speed of 10ft (perfect), as his tiny, nearly-weightless bodies drift upon air currents like smoke or fog particles. He cannot run while flying in gaseous swarm form (unless he possesses a fly speed from some other source), but can maneuver through opening as small as 1" wide at full speed, and can squeeze through spaces as small as 1/4" wide.

Swarm Combatant (Ex)
: At 5th level, the multiplier grows more comfortable in his mastery of the swarm in combat. He adds his Strength modifier to the damage dealt by his swarm attack.

Armed Swarm (Ex): Upon gaining his 7th level in this class, a multiplier learns to make effective use of his equipment, even at such small scales. While in swarm form, he retains his armor bonus to AC, and adds any bonuses he would get to ordinary weapon damage rolls to his swarm attack (such as those offered by a weapon's enhancement bonus, feats such as Weapon Specialization, or from class features). Note that because swarm attacks do not require an attack roll, certain feats (such as Power Attack) are useless in conjunction.

Swarm Split (Su)
: A multiplier of 7th level or higher who is in swarm form and subjected to any single attack which would deal damage in excess of 1/2 his remaining hit points may choose to, in addition to taking the damage as normal, split the bodies that make up its swarm into even smaller ones; a Tiny swarm would become Diminutive, a Diminutive one would become Fine, and a Fine swarm would become gaseous. The multiplier can only use this ability to assume a swarm size he could normally assume with the use of his Swarm Form ability.

Swarmcasting (Ex): A multiplier that has attained 9th level learns to retain fine motor and cognitive control, even as a swarm of miniature versions of himself. He may choose to cast a spell or use spell-trigger or spell-completion magic items while in swarm form. If he chooses to do so, all tiny copies of himself perform the action in synchronization; he is not capable of dealing swarm damage or inflicting creatures with his Distraction ability until the beginning of his next turn. Any spells the multiplier casts upon himself while in swarm form affect him as though he was a single creature and not a swarm; spells and effects produced by others function normally. This ability also allows a multiplier to interact with objects normally (i.e. just as he would in his normal form). He may use Disable Device, Forgery, Heal, etc. normally, for instance.

Infiltration (Ex): At 10th level, a multiplier has reached the pinnacle of many-body mastery. Whenever he begins a turn in gaseous swarm form and shares at least one space with a creature, he attempt to infiltrate that creature's body through any and all available orifices as a full-round action which does not provoke attacks of opportunity. Creatures with no discernible anatomy, such as oozes and creatures with the Amorphous special quality, are immune to this effect; however, immunity to critical hits does not necessarily grant immunity to infiltration - many undead and constructs are affected normally. A creature being infiltrated can resist the attempt with a Fortitude save against a DC of 15 + multiplier's Dex modifier. If the infiltration is successful, the swarm is completely absorbed into the victim's body; no creature has line of sight or line of effect to the multiplier, and any area effects apply only to the infiltrated creature. He perceives directly as the victim does, using any mundane or magical senses as though he was the creature itself. Treat the infiltration like a disease with respect to means of removing it from the afflicted creature; whenever the multiplier is exposed to an effect that would expel him from the infiltrated creature, he can make a Will save to negate the effect (against either the saving throw DC or the Heal check result, as applicable). Once inside, at the beginning of each of his turns, the multiplier can choose one of the following options:
Consume: The multiplier attacks the creature's body systemically from the inside out. This deals 1 Constitution damage (or 10 points of damage against targets immune to the Constitution damage). A Fortitude save (DC 15 + multiplier's Strength modifier) negates this damage.
Control: The mutliplier subtly controls the host's neurons, muscle fibers, hormone glands, etc. in order to control its actions in a limited capacity. The host is affected as if by a command spell, except as follows: instructions to approach or flee treat one other creature the host can perceive as the source of attraction or repulsion, and that in addition to the normal options available via the spell, the multiplier can command the host to make a single melee attack against any one creature it is adjacent to. This effect can be resisted with a successful Fortitude save against a DC equal to 15 + the multiplier's Int modifier.

There is no one right way to play a multiplier. Some may use the extra bodies to easily gain flanking bonuses with oneself. Another may use swarm form to incapacitate their foes, while their allies attack their victims with melee weapons (something the swarm is, fortunately, immune to). Yet another may take a few levels in this class just to gain use of the extra hands for some difficult or otherwise-time-consuming task.
Combat: Multipliers serve less often as front-line combatants, though they may perform more than satisfactorily in that regard. There is no such thing as a 'typical' encounter with a multiplier, but when confronted in a group (such as in an adventuring party), multipliers tend to use their multiple bodies or swarm forms to great tactical advantage, staying simultaneously out of reach of the worst powers and right in the thick of things.
Advancement: The abilities the multiplier gains may not vary dramatically, but at the same time are very open-ended in their utility. Two multiplier characters might look similar on paper, but in actual play may act very differently.
Resources: A high-level multiplier with a martial base and ranks in Use Magic Device can be quite a terrible monster to fight. The mage who has split into four Diminutive versions of herself, then cast mirror image, spider climb, and invisibility can turn a normal magical duel into an instrument of psychological terror. The ranger raining down poisoned arrows in all directions at a target, then controlling the battered and weakened creature to her own ends is a ruthless and efficient tool. The key to an effective multiplier is synergy and strategy.

He... he's alright, I guess. Most of the time. Gotta cut him off a little sooner than the others, though. Get a few too many drinks in him and he thinks he's his own acapella group.
-Dargon Miller, disgruntled barkeep

On the surface, multipliers seem to be just like any other individual; rarely does a multiplier split or assume swarm form in the middle of civilized lands. The few occasions where it did occur did not end well, either for the multiplier (the guard have plenty of handcuffs for all your copies) or for the guard (a high-level multiplier is not easily held by iron bars). Generally, those who make friends with a multiplier react to their abilities much as characters of the world react to any other magic - usually either with disdain or admiration.
Daily Life: Many multipliers take to adventuring, slaking their wanderlust with or without the companionship of others - they are never truly alone, after all. One multiplier might seek out collections of rare treasures, another might seek out ancient secrets; but all the same, the typical multiplier is not content to live a simple life as a farmer, miner, or smith. They thrive on the danger and excitement that adventuring provides.
Notables: Few stories are passed down about legendary multipliers - that is, few stories that identify them as such, or are distinguishable from the illusions of powerful mages or the swarm-shifting abilities of several undead creatures. That said, there are a few legends that could quite easily be based on the stories of powerful multipliers:
Inostari and the Ninja Horde: A notorious assassin known as Inostari was a wanted man for many, many years. Every time a bounty hunter attempted to capture him, even after weeks of tracking careful to get the assassin alone, the encounter would invariably lead to conflict against an ever-growing horde of ninja assassins.
Baribas the Bladestorm Barbarian: An ancient legend tells of a warrior called Baribas, who had survived unfavorable odds in battle countless times. The legends state that when Baribas charged into battle, he would transform into a cloud of miniature whirling blades, tearing opponents to shreds as he moved straight through enemy ranks.
Everywhere Aelriche: A talented battlemage from a recent conflict in a far-off island land, Aelriche gained the moniker "Everywhere" from as-yet-unverified tales of her unique combat tactics. It is said the sorceress could stare a soldier straight in the eyes while a fireball struck him from behind; after a battle, the survivors would often swap stories of their combat trials, and discovered that they had all faced this mysterious battlemage, in different locations at the same time. Whether this is the consequence of crafty teleportation and simply disguising a Stilled spell or the actual use of multiple bodies may never be known to history.
Organizations: Several groups have tried to start multiplier guilds, either locally or in an attempt to unify them across the continent(s). However, the particular mindset that leads to a multiplier is uncommon in itself, and beyond that rarely leads to the sort of one-for-all and all-for-one mentality that guildship requires. There may be small start-ups throughout the world, but no multiplier organizations have ever established a real foothold.

NPC Reaction
As most multipliers prefer to play up the enigmatic nature of their abilities, few are recognized for what they are. Generally, the multiplier is perceived by the public how they wish to be perceived.

The multiplier is somewhat unpredictable. In any given encounter, one may never know if/when they'll choose to split or assume swarm form, and to what degree. It may be difficult to plan encounters when the number of combatants in the party is so variable; it should be safest to assume the multiplier will use his ability and plan accordingly. Note that the simple addition of bodies can affect a great number of encounters, from combat to puzzles and traps. DMs are advised to carefully consider the inclusion of this class into their campaign.
Adaptation: The abilities of the multiplier are fairly concrete, and not particularly specific to any setting or other specific details. While it is certainly possible to adapt the class in some way, any readily-available ways to do so elude the author.
Encounters: Most likely any encounters with a multiplier will be mostly with them as an individual; multipliers are more likely to be loners seeking their own glory, power, prestige, or simply excitement, or charismatic leaders, then as henchmen, servants, or even right-hand-men.

Sample Encounter
The party has been hired to track down and dispose of a mysterious character who has been sabotaging the king's army from the inside. They have finally tracked him down to a makeshift camp in the forest outside of town. As they approach his tent in the middle of the night, aiming to get the surprise on him, they are startled to hear a voice from behind a tree; suddenly, three tiny rogues emerge from hiding, surrounding the party, as the sleeping one wakes and faces them with an evil grin.
EL 7: Ambush! The party is surrounded by four Tiny, dual-dagger-wielding hooded figures.

Dellan Swiftstriker (x4) (split-body form)
Tiny NE Male Human Rogue 5 / Multiplier 7
Init +0, Senses: Listen +, Spot +,
Languages Common, Goblin
AC 21 (+2 size, +3 Dex, +5 +1 chain shirt, +1 shield [two-weapon defense]), touch 15, flat-footed 19
hp 39 (12 HD)
Fort +3, Ref +12, Will +3
Speed 30ft. (6 squares)
Melee +1 dagger +14 (1d2/19-20/x2) or 2 +1 daggers +12 (1d2/19-20/x2)
Full Attack +1 dagger +14/+9 (1d2/19-20/x2) or 2 +1 daggers +12 and +12/+7 (1d2/19-20/x2)
Base Atk +8, Grp +2
Atk Options Sneak attack +3d6
Combat Gear see possessions
Supernatural Abilities flash split, split, swarm form, swarm split
Abilities Str 6, Dex 17, Con 11, Int 12, Wis 10, Cha 8
SQ armed swarm, evasion, lesser amorphous traits, many bodies, one mind, swarm combatant, trapfinding, trapsense +1, uncanny dodge
Feats Dextrous Swarm*, Improved Two-Weapon Fighting, Shapeable Swarm*, Two-Weapon Defense, Two-Weapon Fighting, Weapon Finesse
Skills Balance +20, Disable Device +16, Escape Artist +18, Hide +18, Move Silently +18, Sleight of Hand +18, Tumble +18, Use Rope (with bindings) +5
Possessions +1 chain shirt, +1 dagger (x2), wand of cure light wounds, standard treasure

Bonus: New Feats

Dextrous Swarm
Your skill in moving swiftly within your own swarm works to your advantage.
Prerequisites: Swarm combatant class feature, Weapon Finesse
Benefit: When armed with a weapon compatible with Weapon Finesse and in swarm form, you can add your Dexterity modifier to your swarm attack damage in place of your Strength modifier.

Forceful Swarm

You've learned to put the heft of your strength behind even your swarm attacks.
Prerequisites: Swarm combatant class feature, Strength 13
Benefit: You may use your Strength modifier in place of your Dexterity modifier to determine the save DCs against your Distraction and Infiltration abilities.

Improved Flash Split
You can instantly shatter your body into several copies.
Prerequisite: Flash split class feature
Benefit: You may use a standard action to split yourself into multiple copies as though performing a flash split several times in a row. (Thus, a 5th-level elf multiplier could use this feat to instantly transform into eight Diminutive copies of herself.) When you use this feat to perform flash split in this way, each copy produced gains the benefit of Strength in Numbers only once.
Normal: Splitting into further smaller size categories requires multiple standard actions, and grants temporary hit points for each split.

Multiply Spell [Metamagic]
Your magic affects all of your selves.
Benefit: You can alter a spell with a range of Personal or Target: You so that it affects all splits, copies, etc. of yourself that you currently control as though all individual bodies were targeted by the spell. A multiplied spell uses a spell slot three levels higher than normal.

Shapeable Swarm
Your swarm-self is more flexible than normal.
Prerequisite: Swarm shape class feature, or swarm subtype.
Benefit: You may alter the dimensions of your swarm, so that rather than occupying a single 10ft cube, it may occupy eight adjacent 5ft cubes. The farthest distance from one point in the swarm to another cannot exceed 20ft.