Astyanax: The titular character's magic axe can transform into a spear or a sword when the right power-ups are collected. The spear form is weaker than the axe, but consumes less Mana when casting spells. The sword form is the strongest of the three forms but also consumes the most Mana.
Axiom Verge: Trace's Axiom Disruptor can morph into various different weapons (such as an ice-thrower or a Lightning Gun), as well as project a laser drill, corrupt enemies, and create a remote drone.
BattleZone II: The Scions have shapeshifting Hover Tanks. Combat mode is faster, more maneuverable and regenerates ammo, while Assault mode is more damage-resistance and regenerates health (slowly). The weapons on the tanks likewise shift between Combat and Assault mode; Combat is best suited for fighting other ships, while Assault mode is better at attacking bases or high-end units. The Scion's Arc Cannon for example, goes from firing a long-ranged 5-shot lightning burst in combat mode to a continuous short-ranged lightning arc in Assault mode. International Space Defense Force weapons also have combat/assault modes, but their units are incapable of morphing, forcing them to rely on other units to get the alternate modes.
Bayonetta: This series has the Rodin, weapons that are earned by beating the Fallen Angel of the same name in a brutal Superboss battle. In the first game their default form are four golden rings that look like halos that can morph into any of the various angelic weapons that can be temporarily obtained throughout the game (plus a chainsaw). In the sequel the wrist rings are are now crimson red, and will morph exclusively into demonic weapons, while the golden ankle rings retain the ability to morph into angelic weapons.
BlazBlue: Litchi Faye-Ling's staff can transform into a "stick man" being to attack enemies. It can also split itself into three or double itself to attack from two angles.
Bloodborne: Trick Weapons are the main offensive option for players. These weapons tend to have fairly orthodox normal forms, but can transform into wildly varying alternate forms. This is an odd case, though, as most Trick Weapons are at least seemingly possible in real life — A hand saw that can fold out into a large cleaver, an axe with an extendable handle, a straight sword that can be inserted into a huge stone block to form a hammer, etc.
Control: The game's Service Weapon, a mysterious, psychically-bound tool that can only be wielded by the Director of the Federal Bureau of Control (i.e.: Jesse, the Player Character) and ostensibly works like a gun. Throughout the game, it can be upgraded to change into different forms, each one behaving like a typical FPS firearm, from a simple pistol, to a minigun, to a shotgun, and even a grenade launcher. It also transforms into a sort of key for objects and mundane machinery that only the Director is authorized to activate, and early game documents reveal that it used to have been bothExcalibur and Mjolnir.
Death's weapon Harvester is a Morph Weapon whose Shapeshifter Default Form is a large two-handed scythe. While this is only really shown in Darksiders II in how it splits into two hand-held scythes, The Abomination Vault reveals it can shift into practically any melee implement he wants such as spears, hammers, swords, and even a grappling hook.
Dark Souls III: The Final Boss, the Soul of Cinder, is a manifestation of everyone who has ever linked the First Flame, including every Chosen Undead and Bearer of the Curse who chose to do so across countless player worlds, and he has the variety to show for it. His weapon can turn into a straight sword, a curved sword, a lance/halberd, and a sorcery catalyst. And once his health is depleted, Gwyn and his greatsword come back for a rematch.
Deltarune: Main character Kris experiences this in two ways. The pencils they carry in their "weapon" slot in the overworld inexplicably transform into neon-pink energy broadswords when Kris and their classmate Susie are thrown into the Dark World, and when given the Defend command in battle, Kris takes their sword with both hands and sort of "thrusts" it downward, causing it to morph into a large shield.
In the first game, the Sparda weapon (the ultimate form of the humble Force Edge) works like this, changing from a sword, to a spear, to a sickle, depending on your moves.
Devil May Cry 4 has the most ridiculous example of them all: Pandora's Box, which is a rare projectile weapon version of this — turning into a bowgun, missile-launcher, minigun, laser, buzzsaw, or even a flying missile platform!
In fact, the description of Pandora's Box claims it can take on 666 different forms, although significantly fewer are actually usable in gameplay...
Of course, being Pandora's box the last form, 666, is Dante simply letting it drop open. If the chaos gauge is filled up this does absolutely insane damage, for logical reasons.
Dante's Rebellion sword is cast as this in DmC: Devil May Cry. Rather than have a lot of weapons, you have a sword that is capable of tapping into Dante's Angelic or Demonic heritages, thus changing its form (and each of those states is home to two weapon configurations each that you swap between by using the direction pad).
Traitor, Taiga's weapon in Duel Savior Destiny, has the ability to change its shape to that of numerous other weapons. Taiga's not really sure how it works, but he can turn what is normally a short sword into a longsword, a two handed axe, bombs, a hammer, a three sectioned staff, a trident and a power fist.
Throughout the series, the "Bound Weapon" spell allows for this. Crossing over with Spectral Weapon Copy and Spontaneous Weapon Creation, the spell (classed under the Conjuration school) summons a temporary Daedric weapon for the caster.
In Oblivion's Shivering Isles expansion, there is the sword Dawnfang/Duskfang. It's a blade that changes appearances and elemental alignment (fire and ice) at 6 AM and PM. It's also a bloodthirsty Empathic Weapon that will grow stronger on the next transformation if you kill at least twelve enemies with it.
Eternal Fighter Zero: Sayuri Kurata's Magical Girl wand is capable of transforming into a sword, a gun, a mace, and even a piledriver.
Fate/EXTRA: Technically, the Noble Phantasm of Lu Bu, Rani's Berserker, is one of these. The NP can switch between five different forms, however, because Berserker is under Mad Enchantment, he doesn't have enough frame of mind to use it to its full potential. The only forms he can use in the game are a pike and a bow that launches said pike as the arrow. The other three forms are a mystery.
Rhongomyniad's default form is a lance but it can transform in just about anything. Throughout the game it transforms into Camelot (as in, the actual city), an umbrella, a scythe, a bow, a sentient box, and who knows what else. It may be inaccurate to call it a weapon in the first place.
The Lancer version of Sakamoto Ryouma wields the Amasakahoko, a "key to the heavens". The weapon's default form is that of a two-sided spear, but Ryouma can transform it into anything he wants: he can split it to create two shorter spears, he can turn it into a sword, two swords, an antique gun, an anti-material sniper rifle, and a magical energy blaster. And that's just how he opts to use it; there's no telling what else it can turn into. Oftentimes Ryouma switches between the weapon's various forms in a single attack.
Final Fantasy: The overall series has numerous examples of these.
The Ultima Weapon is a mild variation of this in Final Fantasy VI. It's always a pink lightsaber-looking sword, but it changes size (from a knife to the longest sword in the game) and attack power depending on the wielder's HP total.
Final Fantasy XIII is filled with this. Lightning's gunblade, which is either a gun or a sword, but not both at the same time like Squall's. Sazh's matched pair of pistols can be combined together into a sniper rifle of sorts for some attack animations. Fang's lance can pull apart into a sansetsukon in much the same way.
Mog from Final Fantasy XIII-2 can change between a bow and his moogle form. Then on top of that, while in weapon form, the bow can be closed to form into a sword, in a mechanical method similar to many of the weapons from Final Fantasy XIII. Noel's dual swords from the same game also count; aside from working as two swords (and having a built in sheath for the smaller sword on the larger flame shaped sword), they can also be combined together to form a spear/javelin, which he can throw for ranged attacks or impale for a combo finisher.
Final Fantasy XIV: A large number of the Item Level 70+ gear count as these. Of particular note, is the Artemis Bow, the bard job's relic weapon. While not in combat it looks like a harp. But as soon as it's drawn, it opens up into a full sized longbow.
Guilty Gear series: Millia Rage and her hair. Technically, her hair is alive (long story) and she can use it as a weapon by changing its shape and density at will. Millia can turn it into a blade or shield herself with it, and can shoot a projectile from it, among many other things. Her ultimate kill move has her hair locks impale the opponent. Twice.
Iji: The Komato GEN2 Pre-Loader uses nanotech to assemble its ammo on the fly, allowing its wielder to open fire with anything — from machineguns to death beams to the MPFB Devastator — with absolutely no warning beforehand. The same can be said of the Tasen replica wielded by the protagonist herself.
Jak and Daxter: Jak's Morph Gun. Really, the name says it all; the base gun morphs with the application of mods. Through the use of mods it can become a shotgun, a rifle, a machine gun or a rocket launcher. Gets even more abilities in the third game, where it can fire grenades, beams of electricity, attack saucers, or just plain ol' nukes, among other options.
Keyblades do this in two different ways — first, swapping Keychains gives it a new look based on a certain world or character, with different bonuses in terms of strength / reach / magic. Secondly, they are also capable of Formchanging into a variety of weapons or vehicles.
Kingdom Hearts: Birth by Sleep further establishes that not only Terra can Formchange his Keyblade into a glider; so can his friends Ven and Aqua. Terra can also Formchange his Keyblade into a cannon for his Ultima Cannon Shotlock. The Final Mix version introduces No Heart, an armored Master Xehanort in his prime who can Formchange his Keyblade into shin guards, a large claw, an arm cannon, a floating shield and even a large pair of wings.
Sora finally gets in on the act in Kingdom Hearts III and runs with it — nearly all of his Keychains have their own unique Formchanges. In contrast to the Birth by Sleep trio, his base Kingdom Key doesn't actually transform; it and the preorder-bonus Keychains only trigger a 'Second Form' state that gives him access to some of his toughest moves from past adventures, and the Starlight Keyblade he gets at the Keyblade Graveyard uses a similar Formchange with a new finisher. Every other Keychain (excluding DLC) fully transforms his weapon. Shield? Double crossbows? Bazooka? Gunhammer?Spinning fist? Staff? Claws? Leg blades? Microbots? Spear? Flag? Yo-Yos? The grin on Sora's face during the Formchange transformations says more than words could ever hope to.
Also in Kingdom Hearts III, Lea/Axel is shown to be able to Formchange his new Keyblade, Bond of the Blaze/Flame Liberator, into his old chakrams at will.
The ReMind DLC's data battle against Master Xehanort shows that the χ-blade, the source of all Keyblades, can do this as well, being transformed into giant chakrams, an enormous laser cannon that puts the Lingering Will's to shame, and a Darth Maul-style double-ended blade.
Kohan: Timegate's early 2000 fantasy RTS duology, Rangers have a weapon made of the holy metal Khaldunite. This weapon will go through an animation sequence changing from a glowing sword for melee to a bow that shoots energy arrows when enemies are distant.
The main character, Vayne, has his cat transform into a sword and armor. And then it further transforms into an even larger sword, among other things...
And in the sequel, Mana Khemia 2: Fall of Alchemy, both of the main characters transform their weapons during their Intimate Strikes. Raze transforms his sword of light into a spear, and Ulrika transforms her morning star into a spiked hammer.
Mega Man (Classic): While the weapon itself doesn't change, Mega Man's Arm Cannon can fire a variety of different weapons thanks to the weaponization of his Variable Tools System. In the sequel series, Mega Man X, X's X-Buster does much the same, but, when he gets the inevitable X-Buster upgrade, he can also charge the weapons to get entirely different effects (such as Chameleon Sting, which is stated to fire powerful optic lasers, making him functionally invincible when it's charged up).
Mega Man Star Force: all of your Battle Cards manifest by morphing your Mega Buster into a sword, variant gun, or other weapon. It's just as well that Omega-Xis is a bit of a Blood Knight, since the Mega Buster in the Star Force games is his head.
Mega Man Zero: Zero's Z-Saber can also be a spear, grappling hook, tonfa, magazine for a pistol, or shield you can throw.
In Mega Man ZX and its sequel, the Model ZX biometal (which is based primarily on the Mega Man Zero era Zero) has a single weapon: the handle of the Z-Saber can tilt 75 degrees, turning it into a chargeable buster pistol (this is only really apparent in cut-scenes, however).
Monster Hunter 3 (Tri): The game introduces the Switch Axe weapon class, a "high-tech" armament that can transform using a special phial from a massive axe into a massive sword. Also, Monster Hunter 4 introduces another transforming weapon class, the Charge Blade, which adds a separated sword-and-shield form to the mix.
Enserric the Longsword from Neverwinter Nights: Hordes of the Underdark is a limited version. The weapon can morph itself into few other forms, but after pulling it from its former wielder's fingers, it's stuck in that form.
Paladins: Kinessa's gun needs less than a second to transform from assault rifle to sniper rifle or vice versa.
Phantasy Star Online 2: Zig-Zagged with the Gunslashes. While most Gunslashes change form when they switch between sword and gun mode (usually by retracting the laser blade,) some are Mix-and-Match Weapons instead, keeping the same form in both modes.
Dak'kon's karach blade is shaped by his thoughts; based on your conversations with him, it changes form. The Practical Incarnation reveals that he went through all the trouble of obtaining Dak'kon for the sake of his blade — apparently, only the sky's the limit for how powerful that weapon can become, if Dak'kon is focused enough.
And there's the Entropic Blade, which can be changed into whatever weapon the PC is most skilled with.
Project: Snowblind has a variety of weapons, all of which have secondary fire modes that allow them to fill a role that is completely different from their primary role. Examples include a sniper rifle that doubles as a Mind Control gun, the silenced pistol that can fire smart missiles, and the ricocheting flechette gun, which could unleash a swarm of taser drones. One might say that instead of morph weapons, Project Snowblind has morph ammo.
Shounen Kininden Tsumuji: Tsumuji's weapon, a large shuriken, is able to transform into different weapons against enemies after gaining power stones.
Necrid in Soul Calibur II has a glowing ball of Pure Energy that can become a daisho, zweihander, or battleaxe. He can also do a whip sword or simply expand the ball and smack you with it.
The eponymous swords Soul Calibur and Soul Edge can also change form to fit their wielder. Soul Edge was originally a pair of longswords and Soul Calibur was originally a Chinese jian passed down from Xianghua's mother to her. However, Both swords' most iconic forms are Zweihanders. In most of the games, every playable character has an unlockable weapon that is either Soul Edge or Soul Calibur, morphed into whatever weapon that character uses in their personal fighting style.
Some games feature so-called "Laser Weapon". It can be equipped by any character, even those with drastically different fighting styles. Its description states the it takes on alternate forms to suit its wielder's needs.
Star Ocean: The Divine Force has Elena's "hybrid weapon", which change forms depending on the attack. It can be a gun, a sword, a spear, a whip, a scythe, and a pair of gauntlets. It's unclear if this "hybrid weapon" is the game's implementation of Laser Weapon (which this entry notably lacks), or something else entirely.
Sundered: The Shining Trapezohedron is an intelligent shapeshifting crystal that attacks by coiling around one of Eshe’s limbs and shaping itself into a variety of different blades, fists, and spikes as she swings it around. Its ability to do this is justified by the fact that it is part of an Eldritch Abomination.
Vanquish: The Battlefield Logic ADaptable Electronic weapons system (BLADE) not only transforms into up to three different weapons on command, it can store itself in Sam's arm. How does it work? Who cares?
Wild ARMs 4: Jude's ARM, "Shapeshifter", typically takes the form of a one-handed pistol, but can also transform into a sword, two-handed beam cannon, SMG, or grenade launcher.
Certain Epic quality weapons (before the expansion pack) used to be Morph Weapons (Benediction-Anathema is a good example). This mechanic is no longer used, however, due to problems with enchanting such items.
Another system was introduced instead, the heirloom items. These items can be passed between any character on the same account and server and scale with the characters level. Some of them even change armor type to cover the fact that several classes get a new armor type to use at level 40 (leather->mail and mail->plate).
There's also (with the second expansion) Quel'Delar. Okay, it's always a sword, but in game terms what's far more important is that when it is finally gained after a long quest chain, it "adapts to its wielder" and you can choose what stats it has, which matters more than the actual physical shape it takes. (But if you can't use a sword at all, you'll get a different weapon of equal power from the Argent Crusade's arsenal.)
Xenoblade Chronicles 2: The Torna member Akhos wields one of these after his original Blade Obrona, who gave him dual katanas, dies, which can switch between a bow, a scythe, and a shield. As a Flesh Eater, a Blade who has integrated human cells to gain independence from needing a Driver, this is Akhos' actual original Blade weapon.
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