Riful of the West from Claymore is nothing but these in her Awakened form. She actually uses them for...other things, tough.
And she is not the only one either. Standard Youma often spring spear-like tentacles from their hands, and then there is former #2 "Red Blood" Agatha, first seen in Scene 75.
In an interesting variation, Lucy from Elfen Lied visualizes her telekinetic powers and those of other mutants in the form of long translucent arms. To normal people they are completely invisible, simply causing everyone who gets to close to her to seemingly randomly explode in a fountain of blood.
Pantyhose Taro from Ranma 1/2, whose Jusenkyo form is a two story-tall chimera that resembles a giant ox with wings and sasquatch arms, eventually added octopus tentacles to the mishmash. He can smash through concrete with these, either by jabbing their tips at people, or whipping them down like enormous flails. At one point, he used them to rip a bathhouse's smokestack in half.
The Guardians from .hack//Sign, buggy freudian nightmare monsters from a Virtual Reality MMORPG who not only stab you with their tentacles, but put you into a short-term coma in real life.
Kekkaishi has Princess, a kitsune whose nine tails can be used in this fashion. She's even seen nearly mummifying opponents in them on occasion. Made even more formidable in that they can grow to a huge size.
Karasu from Noein has a power similar to Omega Red, where he has wires as extensions of his body.
Shadow type magic in Mahou Sensei Negima! acts in this manner: creating physical darkness in the form of black tendrils which violently cut things, which one shadow-user Kagetarou used to slice the titular character's right arm clean off. Being that they were in a magic world which had advanced medicinal techniques, he had it re-attached. Recently, a shadow mage has appeared who's so powerful he's capable of pulling Haruna's Cool Airship out of the sky (along with several others). It's explicitly compared toCthulhu.
Naraku from InuYasha mainly fights by turning parts of himself into a mess of these to immobilize, crush, impale or outright devour his foes.
Several of the Angels in Neon Genesis Evangelion. Shamshel has two tentacles instead of arms, Zeruel's "arms" are technically very long, sharp and flexible blades, and Armisael is essentially a giant, glowing-white tentacle.
Several Radam in Tekkaman Blade can spit tentacles. In part II, some of the alien Tekkamen have them as well.
The Maguar from Figure17 fall under this trope, being as their tentacles are in all cases their primary means of defending themselves.
The titular creatures from Parasyte turn parts of their bodies into razor-edge Combat Tentacles capable of slicing through humans like butter.
The Benizakura from Gintama, wielded by Okada Nizou before fusing with his arm like a parasite. He first takes advantage of this by strangling Matako when she talks out of turn. And then later on it gets worse.
The ribbons Wilhelmina uses from Shakugan no Shana are used much like tentacles. Also Shana gets captured in Episode 13 by the twincest twins using vines.
There's a ninja in Basilisk who does the same thing as Wilhelmina. In fact his hair is so strong that when it gets turned against him he ends up suspended in a doorway with all his limbs shattered.
In Saint Seiya, Specters of the Worm (such as Raimi, in the Sanctuary Saga) can use their Surplice'searthworm-like appendages to ensnare, whip, crush, or slice (with sufficient force.) A favorite tactic of this Specter is to burrow underground and let his tentacles burst up to entangle his foe, at which point he'll run a few more tentacles through the enemy.
Luppi's Flower Motif is the ivy. As a result, when he releases his power, he gains 8 powerful vines that can be used as tentacles to capture, crush or punch his enemies. They can also manifest spikes on the end for clubbing an opponent and filling them full of holes at the same time. This power is played straight with him as he's an antagonist.
When Yumichika is willing to release his Coverblowing Superpower, his zanpakutou transforms into a mass of vines that capture the enemy. The vines function by way of Energy Absorption to kill the opponent. By means of Vampiric Draining, it can then use the stolen Life Energy to healing any wounds Yumichika may have received in battle. Yumichika's Flower Motif is the lily, and his vines are full of lilies that collect the stolen spiritual power. Lilies are symbols of death, rejuvenation and beauty. Despite the power, Yumichika's actually a protagonist and not a villain.
Used by the machine designed to implant Mr. Gentleman's consciousness into Junior at the end of ROD the TV to prevent the heroes from interfering with the process.
Shikamaru from Naruto has his "Shadow Sewing" Jutsu, which is basically shadow tentacles. And let's not forget his Shadow Neck Bind. And, of course, Kakuzu has the ACTUAL physical version of these, being basically a human ragdoll.
The host of the 8-tailed demon, an ushi-oni, or, in layman's terms, an ox combined with an octopus, can use this battle style in his fully released state but he seems more fond of spitting out a giant blast of chakra. However, he does often do "partial transformations" where he just has one or a couple tentacles sprout from his body.
After partially mastering the Kyuubi's chakra, Naruto can use the chakra cloak to form arms for use in forming the Rasengan and its variants, eliminating the need for multiple clones.
In Code Geass, Knightmare Frames generally have rocket propelled "Slash Harkens", which are knives/anchors on retractable cables. Its spin-off, Nightmare of Nunnally, however, has Mark Nemo, whose rocket propelled Blonde Knives... float in mid air when they aren't being used, as hair-like tentacles. Zero's cape does likewise.
Ika from Shinryaku! Ika Musume has ten of those (she's a moe-fied squid girl). They are absurdly strong, faster than sound, can reach ludicrous lengths but are also precise to put a string into a needle. And they can regenerate just as fast.
Medusa from Soul Eater has her "vector arrows" function half like Combat Tentacles half like a bunch of spears. Later in the manga, her son/daughter Crona develops these as a part of hir worsening Black Blood infection, with a bonus of creating poisonous thorns that infect people with madness.
When the demonic Yuragi of Mahou Shoujo Ai aren't using their tentacles for... other things, they're breaking bones and punching holes in people with them.
In Saiyuki, Hakkai's demon form has vines that can be used this way, overlapping with Tentacle Rope.
One of the first monsters encountered in Devil & Devil is a weird-ass tentacled monster. These tentacles' main use is to suck time out of their victims, reducing them to cute, helpless infants. The monster can, however, use the tentacles to attack its foes directly. It was offed very quickly though, returning its victims to normal.
Comic book Spider-Man also had Dr. Smythe and son, creators of 'Spider Slayers', as enemies. These always had multiple tentacles used pretty much the same as Doc Ock's. Even if built bipedal with two arms, Spider Slayers would have hidden hatches to throw out extra appendages mid-battle, usually with some kind of trap, such as gas, electricity, webbing, etc.
Spider-Man had for a short time additional mechanical limbs created by Iron Man. Though not as long and flexible as Doc Ock's tentacles, they served a similar function.
And a more minor Spidey foe is the Squid, who is essentially a slender, not especially bright, and organically tentacled Doc Ock.
Venom and Carnage are also capable of using parts of their symbiotes as combat tentacles, as well.
X-Men foe Omega Red, whose tentacles can bash and smash as well as transmit his "death spore virus" (its name changes from one appearance to the next, but he's got a fatal disease he's gotta give to victims periodically or it'll turn back upon him. It becomes his best weapon, though he doesn't appreciate it.)
Jackie Estacado of the Top Cow comic book The Darkness fights with this.
The strictly C-list Marvel villain Constrictor. Think Doctor Octopus...now take away two of his tentacles, put the other two on the ends of his normal arms (taking away the "multi-armed" aspect), and take away the grippy claws on the ends that Doc Ock has... and there you have it, the Constrictor. Now you see why he's considered C-list?
Callisto from the X-Men books. Thanks to fellow mutant Masque, her arms were altered into a set of multiple prehensile tentacles on both sides. She's unique in the fact that she generally used her tentacles to throw a barrage of knives in battle.
Though used more frequently in the Animated Adaptation, Spawn is capable of using both the chains that drape his bodysuit and the tendrils of his tattered, shroud-like cape as this. He particularly enjoys using his cape-tentacles to blind and smother his foes. It's eventually revealed he can do this because the costume is a living being in its own right, and the chains/tatters served a similar purpose for it before it melded to him.
Harry Potter has something like these in A Black Comedy: he learned wandless summoning and banishing spells so well that he can manifest up to six invisible "arms", which can be used to "levitate" (think Doc Oc walking on his tentacles), block spells with handy objects or simply throw them... though their main in-story use is poking Sirius in the eyein retaliation for dumb jokes.
Gurren Solvernia can sprout drills shaped as tendrils when using red spiral energy.
Summer Kelpies are a straight, octopus-style example.
"Sharkface" uses these that look like strips of cloths and seem to have a mind of their own. They're basically immune to magic and shrug off bullets and shotgun shot.
Drake inGone. After Sam burns his arm off, the Darkness (using Lana's healing powers) replaces it with a tentacle.
In Wild Magic by Tamora Pierce, Daine has to summon up a kraken to defeat the Carthaki "pirates" threatening the Swoop.
From Andrew Boland's Hell's Children: "Several bloody tentacles shot out from Offal’s body and proceeded to rap around Z.Y.9.0 and drag him screaming like a child into the nightmare that was Offal. A moment and quite a few screams later Offal threw up a mangled and twitching robot body."
In the short story "Epinikion" by Desmond Warzel, the alien Squids have tentacles that can effect a Clean Cut on a human—and secretions that keep the victim alive for hours after being bisected.
The kossief and shan-kossief from the Icerigger trilogy.
In E. E. “Doc” Smith's First Lensman, we get to see what the Rigellians are like in hand-to-hand combat. They have four tentacle arms with hands on the end, each arm as long and strong as an elephant's trunk. Dronvire goes into a zero-gee battle carrying four space-axes but ditches two of them, using the free arms to grasp space pirates and drag them in to be beheaded, two by two.
Visser Three's tentacle swinging morphs in Animorphs Also possibly the Leeran-Controllers in "The Decision".
These are the main weapons of The Grim in Septimus Heap. The Task of Keeper's Apprentices entails cutting off part of these tentacles.
In the animated music video for Linkin Park's "Points of Authority", an alien race invades a highly technified human outpost defended by robotic soldiers. When the aliens breach the perimeter, the humans activate a machine that causes an entire underground installation to rise up out of the ground and destroy the enemy forces with energy tentacles.
The Tyranids in Warhammer 40,000 have a variety of specialized, weaponized appendages, running the gamut from the flesh hooks a lictor uses to grapple up a cliff, to the feeder tendrils genestealers use to eat your brains, to skyscraper-sized tentacles their living spaceships use to break enemy vessels apart. Quite a few of them are also bladed.
Daemons of Slaanesh have weaponized Naughty Tentacles, and given their nature it can quite difficult to tell how they're using them at any given time.
The Dungeons & Dragons spell "Evard's Black Tentacles" can summon a bunch of these. Also in D&D, Displacer Beasts have two hook-tipped tentacles for tearing things apart.
D&D has tentacles by the bushel: krakens, mindflayers, phantom fungus, otyughs, chaos beast, many of the Elder Evils, and dozens of others in too many splatbooks to list.
Players can get in on the Combat Tentacle action with a feat from the Lords of Madness (Book of Eldritch Abominations) source book. The Aberration blood feats represent a character having a common ancestry with Eldritch abominations, and the aberration blood feat Deepspawn causes the player to sprout two tentacles which can be used for attacking.
1st and 2nd Edition monsters with damaging tentacles
aboleth (4 tentacles), froghemoth (4 tentacles), giant octopus (8 tentacles), kampfult (6 tentacles), the kraken (10 tentacles), the mihstu (4 tentacles), storoper (6 tentacles), xag-ya and xeg-yi (6 tentacles) and yochlol (8 tentacles).
Additionally, She Who Lives in Her Name (and some Infernals) has a psychic version of this, producing tendrils of solidified force to fight, pick things up etc. They 'looks' and acts like a Diclonius' vectors.
Tsk, tsk. Are we seriously forgetting the Celestial Circle spell Magma Kraken?
The queen of all offensive tentacles however, is Kimberry, better known as The Sea That Marched Against The Flame. She can create tentacles out of any liquid, including spilled blood. And they are deadly poisonous. Her shintai charms turns you into giant monster made of very naughty tentacles, i.e. a shoggoth.
Many enemies, like Garradores or Gigantes in Resident Evil 4 sprout "tentacles" (Actually the Plaga inhabiting their body) when hit hard enough. Also, Plagas will randomly grow their tentacles out of an almost-dead Ganado. And Resident Evil 5 gives uns Uroboros which is basically nothing but a giant wriggling mass of Combat Tentacles.
Osmund Saddler also uses one to kill Luis, and sports a different one during the final boss fight.
Ultros, from Final Fantasy VI, a recurring joke villain with an impeccable sense of timing.
A writhing, sentient mass of tentacles which entangles the engine room of Figaro Castle and prevents it from returning to the surface. The tentacles can ensnare individual characters and drain their HP.
The Final Fantasy XI playerbase has many bad memories of the Sea Horror, a 60+ monster that, while very beatable by most jobs at 75, almost always spawns when the highest level player in the area is around level 30. Fun times.
Mainstream Carnage can also put you under wraps, though being much more Ax-Crazy than Venom (and given some of Venom's finer moments, that's saying something!) he's just as likely to make 'em pointy and impale you.
The Memory of Richard Grady, a boss from Silent Hill Origins, has several tentacles hanging from the ceiling as Travis fights it. If you're too close to them, they'll loop around Travis's throat and attempt to strangle him. Also, in Silent Hill 2, the final boss does this as well, only with some kind of scorpion tail.
...and its The Legend of Zelda: Ocarina of Time predecessor, Morpha, the giant amoeba who poses as water until you get close and its tentacles getcha (think that creature from The Abyss, only evil). Morpha's inspired a lot of Rule 34 art.
World of Warcraft has more than one tentacled horror, although in general they stick to oversized humanoids for their dungeon monsters.
Notable example would be the raid boss C'thun (a literal Giant Eye Of Doom), who in addition to having a nasty one shot kill eye laser, spawns tentacles, eye tentacles that fire Eye Beams and giant versions of the two. One of the items he drops is the Vanquished Tentacle of C'thun, which allows the player to summon his very own combat tentacle to attack an enemy for a short time.
While the attack on the tentacle has been sadly outleveled into oblivion, some people still use itfor kicks.
C'thun's spiritual ancestor, the unnamed Forgotten One in WC3, also spawned tentacles.
Yogg-Saron, end boss of the Ulduar raid dungeon, also appears to use tentacles as weapons. It seems like there's a theme developing here around the Old Gods...
Having noticed the popularity of the Vanquished Tentacle of C'thun, Blizzard introduced an improved version, the Vanquished Clutches of Yogg-saron. The concept's the same, but now it can summon 3 types of tentacles! One of them shoots acid.
Continuing the tradition, the BFS Gurthalak, Voice of the Deeps, has the ability to summon a tentacle that will cast a very powerful Mind Flay on your target, sometimes more than once.
The Magus in Warhammer Online: Age of Reckoning can extrude a massive tentacle from his disc (yes, disc) to swipe across enemies' faces. The Marauder class may come under this also, as his arm can be mutated into a variety of goopy shapes, some more tentacly than others, but all quite nasty.
The Zerg base defenses, Sunken Colonies, attack with a giant burrowing tentacle.
The Sarlacc in Return of the Jedi probably didn't get much to eat on Tatooine. The Force Unleashed has another one on Felucia, and that one has grown much bigger, slapping at you with arms 3 meters in diameter.
A couple of City of Heroes giant monsters - Lusca (big octopus) and the Hydra (big slime thing) both spawn extra tentacles to fight with. The Hydra is so damn big its tentacles can attack you from anywhere in the thousands of meters of tunnels making up the abandoned lower level of the city sewer network.
Also evoked by a few powers. The Plant Control ability Carrion Creepers causes huge vines to sprout from the ground and lash at enemies, and the summoned pet Fly Trap from the same set attacks with whip-like vine arms. And, of course, there's the Dark Blast power Tenebrous Tentacles.
One of the Sai units in the game Stormrise can generate energy tentacles from their lower arms to clobber their enemies with. They can also learn to electrolute said tentacles, further increasing the damage they do.
When she's not forming blades with them, Morrigan from Darkstalkers Sometimes use her wings/bats as these (see her standing and jumping Fierce Punch attacks). This is made much more explicit in the anime OAV, when she's shown using them like that in a fight. Not to mention the official names of the said attacks are apparently stuff like Orgasm Wire.
In Skies of Arcadia, the final bosses' most devastating attack involves you being paralyzed, lifted, and impaled by fluid tentacles and blasted by the creature fused with him.
Early promo shots and concept art for Half-Life 2 featured translucent blue tentacles bothering the leads. The tentacles would've been the surface manifestation of a huge under-ground being bothering City 17. Ultimately it was decided that it just wasn't a fun opponent.
In Dead Space several necromorphs have these. The lurkers are infected infants with three tentacles; which can either shoot spikes or tear into a foe that they latch onto. Guardians are corpses stuck to the walls; immature guardians can only flail their intestines at Isaac, but advanced ones can shoot out pods with tentacles similar to the lurkers. In addition, if Isaac gets too close, the lurker will decapitate him. There are also tentacles which grab Isaac around the legs; if he doens't break free in time, they'll drag him to a gory death sequence. Finally, all three bosses (the Leviathan, the Slug, and the Hive Mind) all use these as their primary means of attack.
The Broodmother from Dragon Age: Origins is stationary, but has four tentacles that can pop out of the floor to make life difficult for ranged characters.
It also has a number of larger, thicker tentacles that it can use to grab anyone closing in melee. It then violently shakes them and vomits poisonous bile all over them.
Rise Of The Kasai features this as a reoccuring boss type; tentacles from an underground monster will burst out in a large area and the player has to hack them apart one at a time. Some are thin grabbers, some are spiked with mace heads, some are armored, and one has a grasper, or possibly the creature's mouth.
Quite a few monsters in Dominions, what with it being the universal grab bag of mythologies it strives to be. Krakens, bukavacs, void lords, you name it. Oddly enough, aboleth ones are just for show - guess you don't really need base, squick weapons when you can turn brains into quivering goo at will.
The Kayran in The Witcher 2 Assassins Of Kings is a mutant hybrid with disproportionately huge mouth tentacles attached to a smaller, crab-like body. It attacks by slamming these tentacles to the ground, using them to throw rocks and whipping them across the entire battlefield (allowing the player to grab hold with a quicktime event).
Cuttlefish in Battle for Wesnoth. Heck, there's even a monster called Tentacle, which is described as the tentacle of a larger, unseen monster.
The final boss of Borderlands has two sets of tentacles. There are four purple flailing tentacles which shoot explosive spikes and two red tentacles which are slammed into the ground to create shockwaves.
The demonic foliage in Dark Souls have these in place of arms. The Pisaca in the Dukes Archives have this on their head, which they use to restrain you and deliver an extremely deadly attack.
The World Ends with You has a Jellyfish Noise that will attack you (or your partner) with its tentacle to violate your HP. Says so in the description.
"If you're not careful, that obscene tentacle will start violating your HP!"
Disgaea 4: A Promise Unforgotten has Desco, who mainly attacks with the tentacled creature on her back. She can attack directly with them, shoot beams from them, or temporarily detach it from her in order to transform it and attack enemies with them.
Both The Darkness games have shadow combat tentacles. They become more powerful in the second game, offering several brutal methods of instant killing enemies.
Dungeon Crawl has the option of playing an Oktopode who can constrict up to eight oponents with these (though that is rarely a good idea). The spell Beastly Appendix can allso give you these.
In The Elder Scrolls V: SkyrimDragonborn, Miraak wields a staff that summons tentacles from the ground, wields a sword that turns into a tentacle when he swings it, and randomly sprouts tentacles around him when he is attacked. Appropriate, given that he is a servant of Hermaeus Mora.
The final boss of KickBeat attacks you with tentacles. Some are accompanied by dark energy spears that appear in place of the power-ups that normally float over some of the mooks' heads in the other levels, and missing on a double-tap note will incur damage even if you destroy the tentacle with the first beat.
Some were seen in a battle near the final one in Adventurers.
Howard the Tentacle Beast in Tales Of Gnosis College suddenly manifests powerful tentacles with razor-sharp edges when a human being he cares about is threatened. The series also contains an panel in which a character imagines huge tentacles wrapping up and attacking an aircraft carrier.
Carmilla (Sara Waite) in the Whateley Universe works of fiction. Not too surprising given that her father is Gothmog, demon of lust, while his mother is Shub-Niggurath - and she's related to Cthulhu on her mother's side. She can launch tentacles out of any part of her body, and those tentacles may then have mouths or eyes or worse if she wants. She has killed several people (and a LOT of animals) by thrusting her tentacles into them and eating their souls. She has used them as Naughty Tentacles too: at least one side character is now pregnant from this. Oh, by the way, she's one of the good guys in this universe.
Nergal and Junior from Billy and Mandy have retractable tentacles that can shock people with jolts of electricity and even mutate people by zapping them with red energy.
Doctor Drakken from Kim Possible got an equivalent to these with his mutant vines, using them in one scene to crush an enemy gun.
Waterbenders in Avatar The Last Airbender frequently use a form of this that involves surrounding themselves in water that they extend into tendrils (fittingly called the "Octopus Form"). And at one point, a waterbender actually uses vines as combat tentacles, by bending the water in them.
Transformers Prime has Soundwave, who used his tentacles to hack a radio telescope and fought the humans from a distance when they tried to block him out of the network. He's also used them to bore through solid rock, and attempted to do the same to Wheeljack, but failed, and settled for using them to pick him up and throw him around... by the head. He's yet to kill anyone with them, but in both instances, he demonstrably could have had he not moved on to the next mission objective instead.
The Teen Titans encounter these on a pretty regular basis. Alien police bots, various goo monsters, and anyone passing by a supervillain garage sale have some of these. Even Cyborg and Raven on occasion.
Alpha from Men in Black: The Series, who grafts alien body parts onto himself.
On Futurama, Bender's jointless arms can twist and coil as freely as tentacles, and are certainly strong enough to invoke this trope if necessary. Subverted in that he's more likely to use their enhanced flexibility to pick your pocket than kick your ass.
Batman Beyond's shapeshifting blob Inque uses this as her primary method of attack and they're stronger than steel, no less, though in some instances, her body usually slides into either one single, thick tendril or a plethora of them at once.
Played straight with Jellyfish and Anemones who line their tentacles with Cnidocytes (stinging cells) that deliver toxins into their prey. This system is so effective that they usually just wait for the prey to come to them.
An elephant's trunk functions very much like a tentacle in its muscle mechanics, and can be quite a dangerous weapon.
Constrictor snakes, such as boas and pythons. Their whole body will act as a tentacle to wrap around the body of the prey.