Detailed below are two ways of doing this in Hero System, Fifth Edition (2002).1
The power Duplication (101–3) usually allows a character to create only exact copies of himself. However, the power has available a unique power advantage Altered Duplication that ranges in value from +¼ to +1 to permit the character to create duplicates that are anywhere from 25% to 100% different from the original. Combining this power with the power Mind Link (132–3) is probably good enough for simulating a hive mind. Going beyond that may lead to developing really complicated powers involving the character's normal senses modified by power advantages like No Range Modifier (+½) (272)—which the game specifically says not to do—or an overwhelmingly expensive version of the power Clairsentience (93–4), likely modified by the power limitation Always On (−½) (182).2
The default way the power Duplication works is that the character wills the copies into being using whatever special effect the player chooses, in essence the power functioning a little bit like the primary superpower of Marvel Comics' Jamie Madrox (frequently of the X-Men) except on a vastly reduced scale.3 However, unlike Madrox and more like DC Comics' Triplicate Girl of the Legion of Super-heroes, Hero System, Fifth Edition characters must take care of their copies: if a copy dies, it dies like any other character, and the base character is typically out the character points spent on that power forever.4
Like I said, that's the default for the power Duplication, but a character can put on the power the unique power limitation Cannot Recombine (−0) (103) that essentially lets the player just play multiple (different or similar) characters: the player's character simply pays the character points for the player having the privilege of running multiple characters. Add to the characters the aforementioned Mind Link power, and so far as I can tell simulating a character such as Harem from the Web comic Grrl Power shouldn't be a big deal.
It should come as no surprise that there's a significant downside to the Duplication power: It's enormously expensive. It typically costs a character 1/5 of the character's total character points to create but one duplicate. However, after the initial Duplication power's cost is assessed, another +5 points yields 2× the number of copies (i.e. 5 points allows up to 2 copies, 10 points allows up to 4 copies, 15 points allows up to 8 copies, etc.). Combined with the aforementioned power advantage Altered Duplicates (+¼ to +1), one player could see his character become a team unto himself, and—unlike Marvel Comics' the Collective Man—see each "copy" have totally different abilities.5 In this way, the power Duplication could be used by player to simulate a character like Swarm—Marvel Comics' Nazi made of bees5—, but I don't recommend it: Swarm has thousands of bees he can expend, and his powers—in this reader's opinion—are somewhat better simulated as described below.
(It's been mentioned that the power Duplication is absent from one or more editions of the Hero System. I know that the Duplication power is present in the game's second through fifth editions, originally appearing in Champions III (1984) (27–8) for second edition. It's a shame if the power were dropped for Hero System, Sixth Edition.)
When a player's concept necessitates eventually-replaceable lesser minions, those are best purchased using the perk Followers (58). The Followers perk specifically says
A character can have 2× as many Followers for +5 points. These additional Followers do not have to be identical to the first Follower; one can be, for example, a human squire and the other a well-trained horse.
This GM has allowed players who express a certain vision for their characters—contrary to rules—to apply power advantages and limitations on the Followers perk. Further, he's allowed Followers to buy powers like Extra-dimensional Movement (111) and Mind Link—instead of making the base character do so—to simulate abilities like the base character being able to bring forth the Followers spontaneously (rather than literally following around the base character) and the base character being able to issue undetectable silent commands to his the Followers from afar.
In this way the perk Followers can be used to simulate, for example, Charlton Comics' Mr. Jigsaw and M. F. Comics' Captain Marvel, both of whom possess the disturbing power anatomic liberation: the ability to detach body parts yet still have them function independently.6 More prosaically, in this fashion the Followers perk can be used instead of the Duplication power to simulate any character that can bring forth decidedly lesser characters like the Decepticon Soundwave of the Transformers toy line, a robot/cassette player that carries within it littler disguised-as-cassette-tapes robots like Ravage and Rumble. Further, Swarm—mentioned above—could have several followers of varying sizes representing successively smaller collectives of bees. (These are collectives for convenience and ease of use. Although the typical character that has 250 total points available could have spent all those points on 562,949,953,421,312 25-point followers—and, really, I think that's enough bees—, actually doing that would yield a weird and unplayable character.7)
The huge advantage of the perk Followers is its cost: There's no minimum cost for the Followers perk like there is with the power Duplication, and, also unlike the Duplication power, no power advantage is necessary for having Followers with different statistics. However, technically, Followers are supposed to be NPCs—fiercely or even robotically loyal NPCs, but NPCs nonetheless—, and this makes them technically vulnerable to the thousand natural shocks that NPCs are heir to. Further, convincing the GM that this is, in fact, the best way to simulate the character's powers may be a challenge. Creation of fractional forms—to this GM, anyway—sounds much more like the perk Followers than the power Duplication, but because each 1 character point yields 5 character points in the Follower with no minimum (although there's a practical maximum of the base character's own point value), this GM can understand how another GM may disallow this method of simulating a character that's really several characters as just too shady.
Hero System, Fifth Edition is vast, though, and above are only two of many ways that a one-mind-many-bodies or I'ma-gonna-leave-this-eyeball-here-so-I-can-see-what-happens kind of character can be simulated. I've not mentioned things like the power Transform (152–4) that with the GM's permission can be used to spontaneously create anything, including copies of the character, robot spies disguised as cassettes, or bees. I've also only mentioned in passing the power Extra-dimensional Movement (111) that, for example,—and, again, with the GM's permission,—could see the player picking a wildly improbable dimension that is populated solely by copies of himself (and, perhaps, his grandson) that the character can recruit to aid him in his quests, or that could see the player picking a dimension (undoubtedly an evil dimension) comprised wholly of bees then giving the character the power to control insects.
In other words, I recommend that you describe the character's powers to the GM and ask the GM how the GM would prefer the character's powers to be simulated. Then, if the cost of such powers exceeds the vision you have of your character, either dial down the powers and play the character until he's earned enough experience points to do the awesome stuff you imagine (let's hope it's less than 40 years!) or propose to the GM a less expensive alternative like one of the above or resign yourself to playing a different character. Keep in mind, though, that having multiple sets of actions under your direct control—even if they're just the actions of a few trillion bees!—is never cheap.
1 Anyone else with a Hero System, Fifth Edition rulebook should treat it with some respect. Look at how much folks are asking for it on Amazon.com. Good heavens!
2 A GM that mandates that the character possess that super-high-priced Clairsentience power—rather than allowing the Mind Link power as a workaround—is probably telegraphing his discomfort with the whole character concept. That's valid: While the wargames from which RPGs originated allowed controlling whole armies, RPGs traditionally limit players to one PC per player. To be sure, several characters under direct player control is a different paradigm for both the player and the GM. In other words, steel yourself for the GM to ultimately reject your character, be it because the character's too complicated, too distracting, or some other reason. Just sayin'.
3 Madrox has been around for over 40 years and has seen his initially rather pedestrian superpower—his only superpower, him otherwise being a regular dude—metastasize in a shocking number of ways, including its weaponization. For instance, Madrox has exploded a foe by creating a copy of himself inside that foe!
4 In some continuities, Triplicate Girl sees one of her two copies die. In the wake of that tragedy she changes her superhero name to Duo Damsel. I kid you not.
5 In the comics, it's rare for a character to have a superpower that enables him to spawn beings that aren't duplicates of itself. I know there's at least one character in the Marvel Universe with comic-book-style evolution powers (and I'm not misremembering DC's Evolvo Lad!) who can, while his base form continues to exist, simultaneously bring forth both an evolved and a devolved version of himself, the former super-smart with psionic powers, the latter apelike with super-strength. However, the character's name escapes me. (Help me, Comments!)
6 Still not kidding.
7 Someone somewhere just said Challenge accepted! I pity his GM.
8 This is unlike the anatomical liberation power of DC Comics' Arm-fall-off Boy, who, while capable of detaching his limbs, can only use them as them clubs. Seriously, I couldn't make this up.