Bladesinger

The Bladesinger is a Dungeons & Dragons gish class associated with the elf race, and particularly the elves of the Forgotten Realms. To many, it is seen as a source of skub, with even shameless elf-aficionados often regarding the original lore for the class as cringe-worthy.

At its basic concept, the bladesinger is an elven warrior-wizard with some bardic overtones, who learns to simultaneously fight in melee and cast spells. Members of an elite society, bladesingers are supposed to be dedicated to the protection of elves and the preservation of elf culture.

AD&D

The very first appearance of the Bladesinger was in Advanced Dungeons & Dragons, as one of the kits provided for elf fighter/mages in the Complete Book of Elves.

The AD&D Bladesinger is an elf- and half-elf-only kit that requires 13s in Strength and Constitution and 15s in Dexterity and Intelligence, as well as the base class of fighter/mage. A bladesinger chooses a single iconic weapon, which must be a one-handed weapon or a versatile (can be used with one hand or both hand) weapon. They get +1 to attack rolls and damage rolls with this weapon - which stacks with the +1 for being an elf armed with a longsword or shortsword, but not with anything else - but suffer a -1 penalty to all other weapons, which stacks with normal non-proficiency penalties, and lose their normal elven aptitude with a bow.

Their training manifests in three special ways. Firstly, bladesingers get a +1 bonus per 4 levels to all attempts to perform a special combat maneuver, which mostly serves to negate the normal penalties for trying a disarm attack or whatever. Secondly, they can still defend themselves whilst casting a spell, with an AC bonus to frontal attacks whilst spellcasting equal to level divided by two, plus one, and with fractions rounded down. Finally, they have mastered the art of casting with only one hand, although this still increases all casting times by 2.

For hindrances... first and foremost, they're supposed to advance elven causes and protect elves whenever possible, and failing to help an elf is a huge social blow - thankfully, unlike the Paladin, this doesn't result in direct powers loss. For another major weakness, although they have better martial training than most fighter/mages, they can still only wear elven chain, studded leather, or lighter types of armor without penalty; anything heavier than this inflicts a -2 penalty to their attacks. Finally, they can't use either shields or two-handed weapons; they need at least one hand free to cast with, after all!

3rd Edition

In 3rd edition, the Bladesinger is presented as a 10 level long Prestige Class only accessible to Elves and Half-Elves. It requires a Base Attack Bonus of +5, 4 ranks in the Concentration skill, 3 Ranks in the Perform skill (Song and Dance), 3 ranks in the Tumble skill, the feats of Combat Casting, Dodge, Expertise, Still Spell, and Weapon Focus (Longsword or Rapier), and the ability to cast 1st level arcane spells.

Bladesingers gain proficiency with Light Armor (though their class features are useless in anything heavier), an array of new spells per day of 1st through 4th levels, three bonus feats from a special list (Any Metamagic, Combat Reflexes, Improved Critical (Longsword), Improved Disarm, Mobility, Quick Draw, Spring Attack, Whirlwind Attack), and five "Songs".

Bladesong grants a Dodge bonus to the Bladesinger's AC equal to their Intelligence bonus, so long as they have one hand free and are wielding a longsword or a rapier with the other.

Lesser Spellsong means that when a Bladesinger benefits from Bladesong, they also gain the ability to take 10 on Concentration checks when casting defensively.

Song of Celerity means that when a Bladesinger benfits from Bladesong and uses the full attack action, they can also cast any arcane spell with a casting time of 1 action or less as a free action. Which, coincidentally, also covers their iconic "bladesinger spells" like

Greater Spellsong means that Bladesingers ignore the arcane spell failure chance of Light Armor.

Finally, Song of Fury means that when a Bladesinger benefits from Bladesong and uses the full attack action, they can choose to inflict one extra attack that round, at the cost of inflicting a -2 penalty on all attacks that round.

4th Edition

In 4th edition, the Swordmage was introduced in the Player's Guide to Faerun as a spiritual successor to the Bladesinger, only with pretty much none of its original fluff. The Swordmage was described as an Arcane Defender; a warrior-wizard tradition that specialized in the use of one-handed weapons and spells that augmented its defense, boosted its mobility, and gave it lots of elementally charged or mystically empowered attack options. Want to Force Choke a bitch? Throw your sword and turn it into a ricocheting lightning bolt before summoning it back to your hand? Sketch sigils in the air with your sword that make fuckers explode? The Swordmage had you covered.

Still... even with the fluff that it was very popular amongst eladrin, the Swordmage wasn't a "true" conversion of the Bladesinger of old. So, when Essentials took over and WoTC released the Neverwinter Campaign Setting, they introduced a new Bladesinger class. This was an Arcane Controller, a Wizard variant that was noted by fluff should be restricted to eladrin, elves and half-elves, and which keyed its abilities off of Intelligence and Dexterity, in contrast to the Int/Str focus of the swordmage. Its major difference to a wizard was its class features, which mechanically supported the idea of a warrior-mage who forsook armor but wielded a one-handed sword instead of a traditional wand or staff.

5th Edition

In 5th edition, Bladesingers reared their heads once again as a new Arcane Tradition (subclass) for the Wizard in Sword Coast Adventurer's Guide, the dedicated Forgotten Realms splatbook of the edition. As with 4th edition, WoTC notes that traditional fluff decrees it should only be available to elves and half-elves, but it doesn't mechanically enforce this trait. Indeed, it outright encourages DMs to ignore that angle, either to run their preferred take on the realms or to transplant the Bladesinger to their own homebrew settings.

ts 2nd level feature is Training in War and Song. This gives it Proficiency with the Performance skill, light armor, and a single one-handed martial melee weapon of the Bladesinger's choice. Swords are iconic, but as the sidebar notes, there's all kinds of styles, including axes, hammers, picks and whips.

Its other 2nd level feature is Bladesong, the big "special attack" of the class, an ability to enter a state of supernatural speed, agility and focus as a bonus action. You can't use it if you're wielding a shield, or if you're wearing medium/heavy armor. Likewise, it can be ended early if you take up a shield, put such armor on, make a two-handed attack with your weapon, or are just incapacitated. So stick to the light armor and one-handed weapons if you wanna use it. You can use this feature twice per short rest, and unless ended early (which you can do voluntarily), it lasts for one minute. Whilst in Bladesong, you add your Intelligence modifier (min bonus is +1) to your Armor Class and to any Constitution checks you make to concentrate on spells, you increase your walking speed by 10 feet, and you gain advantage on Dexterity (Acrobatics) checks.

A Bladesinger gains the Extra Attack feature (attack twice when you use the Attack action for your turn) at level 6.

10th level unlocks the Song of Defense ability; whilst in Bladesong, a Bladesinger can expend spellslots when they take damage, reducing the damage by (spellslot level multipled by 5).

Finally, 14th level unlocks the Song of Victory feature, where Bladesong causes the Int bonus to apply to damage from the Bladesinger's melee weapon as well.

All in all, the 5e Bladesinger is not necessarily a bad subclass, but the fact it's got such a schizophrenic design - class features orientated towards melee combat, but wizard spells are predominantly aimed at being used at a distance - that it suffers, particularly when compared to the Swordmage of 4e, who had an entire arsenal of thematically-supporting close- to medium-ranged spells to back it up. It's telling that every fanmade guide to Bladesingers out there exhorts the player to grab the small handful of Swordmage spells that were officially converted to 5e as part of the Bladesinger's spell arsenal.

From another perspective, it's consistently the hardest class to kill in game beating out even eternal favorites like the abjuration/fighter dual class. The main conceit is not getting hit and instead using an AC that without reactions or bonus actions hovers at 20-24. Taken with the Elemental Evil Player's companion available for free (Absorb Element Spell), shield, blur, invisibility, mirror image or other defensive spells of your choice you become one of the best tanks in your party if not the best. All with the utility and insane late-game capabilities of a wizard. (Remeber you're a wizard who also swords, not a fighter who also knows spells, that would be an eldritch knight.) You're damage also remains consistently relevant. When our party fought a hill-giant early at level-3 I was the sole member in melee because I was capable of raising my armor class to what was effectively 30-40 for the entire fight and forcing the giant to stay away from my squishy teammates. though it burned all my (few) spell slots. It should be noted that our GM fudged the hill-giant an extra 30 health because the delve was going 'too smoothly'. Mind you, unless you rolled spectacularly well during charcter creation (19's in both intelligence and dex your AC won't be as high as early.)