New subclass, criticism appreciated.
(edit: <hopefully> clearer language, cited non-bard necromancy spells to facilitate evaluation)
College of Discord:
All bards learn how the magic of harmonics can aid their allies and hinder their opponents, but bards of the College of Discord prefer to focus on how dissonance can just as easily influence minds... usually in negative ways.
Bonus Proficiency: At 3rd level, you gain proficiency with the Intimidate skill and martial weapons.
Howl: At 3rd level, you have learned to scream like a banshee to unnerve your foes. As an action, spend and roll a Bardic Inspiration die, and select a number of creatures equal to the result who are within 30 feet of you, and can hear you. Each creature must succeed on a wisdom saving throw versus your spell save DC, or become Frightened of you until the end of your next turn.
If the creature cannot hear you, or is immune to the Frightened condition, it is not affected by Howl.
Dirge: Beginning at 6th level, whenever the bard gains new spells or replaces them upon leveling up, he may choose any spell from the Necromancy school appearing on any class spell list. A spell you choose must be of a level you can cast, as shown on the Bard table. The chosen spell counts as a bard spell for you.
You may also choose any cantrip from the Necromancy school as the cantrip you gain at 10th level.
Spell Level: Spells
Cantrip: Spare the Dying, Chill Touch
1: False Life, Inflict Wounds, Ray of Sickness
2: Gentle Repose, Ray of Enfeeblement
3: Animate Dead, Vampiric Touch
4: Blight
5: Contagion
6: Harm, Circle of Death, Create Undead, Magic Jar
7: Finger of Death
8: Clone
9: True Resurrection, Astral Projection
Cacophony: At 14th Level, you have mastered the art of dissonance. Add your Charisma modifier to the damage roll of any spell which causes necrotic, thunder, or psychic damage.
You've got a decent skeleton here, but some of the abilities don't quite sound right. Like the Howl ability. Why does it modify the DC using the Bardic Inspiration die it burns? This is the only ability that does this, and it's a level 3 ability, meaning their DC just spiked and became almost impossible for a lot of creatures to get around. I'm not amazing at understanding rules balancing, but that sounds kind of broken, even if it is only about 3-4 times per day. Not to menton, there's a simpler way to do such an effect. "At 3rd level, you learn to scream like a banshee and unnerve your foes. As your action, you may expend one of your Bardic Inspiration Dice and choose a target. The target must succeed a Wisdom saving throw against your Spell Save DC to resist this ability. On a failure, the creature may only use its turn to move as far from you as possible, using its action only to perform either the Dash or Disengage Actions. The target may attempt this saving throw again at the end of each of its turns, ending the effect on a success. Creatures immune to the Frightened Condition are immune to this ability."
Dirge is basically a free rehashing of the Lore Bard's Extra Secret feature, you may wish to change this. Perhaps give them an ability that modifies or supplements Necromancy spells that they cast? Or even lets them learn another cantrip of their choice that's thematic to the class option. The final ability is pretty cool, but a bit lack-luster compared to what Sorcerers and Wizards get at that level.
I appreciate the input, and will consider modifying as I receive more. These are my thoughts on the abilities and some responses to your suggestions:
The Lore and Valor uses of Bardic Inspiration dice are guaranteed to have their effect occur. I loaded the BI die on top of the Spell Save DC to make it more reliable. The effect as written is so that it isn't too... effective... as a free crowd control at a low level. My version is higher reliability / lower effectiveness, yours is lower reliability / higher effectiveness. Fair trade off, and yours is simpler language. Waiting to hear from others.
Dirge grants them the ability to choose Necromancy spells each time they gain new spells, not just at level 6, 10, 14 and 18, though it does not provide additional spells as Level 6 lore bard.
Cacophony, because I didn't want to front load damage boosts, and because damage isn't really the bard's main pursuit anyway, hence it coming much later along.
Hmm... Well you make a good argument for them, the only thing I can say is probably altering Dirge's language to better convey that it lets them actually learn necromancy spells like "Starting at 6th level, you study ways of greater connecting with undeath. At this level and every bard level beyond, when you learn a new spell or choose to replace a spell that you already knew, you may pick from any spell from the Necromancy School to learn. You must be able to cast spells of the spell's level to learn it." I don't know if that's a good way to write it, but it seems to get the point across.
OK, we're all thinking it, so:
Treantmonklvl20 wrote:
In regards to Howl, you could just reflavor Turn Undead. Instead of it targetting all undead, it targets a number of creatures equal to the Bardic Inspiration die that can hear you and uses the relevent text of Turn Undead to determine whether the target saves or fails. This way, the BI die is useful and can help weed out some enemies.
Using the BI die as a means to setting how far they move away is artificial and feels wrong. If you scare them, they should try to move as far away as possible, not some arbitrary number of feet.
Also, since you are all about discord and necromantic fluff, undead targetted should get advantage on the saving throw, since they "feel your vibe." 
Also, so you aren't necessarily stepping on the toes of any Clerics or Paladins in the party...
Something to consider; the Howl ability shouldn't work on creatures that are deaf. I'd recommend changing the stipulation at the bottom to "A creature that cannot hear or become Frightened is immune to this ability"
Love the basic concept, but not sure about the mechanics.
Why martial weapon proficiency, for example? It feels to me like a wish-list feature, as in "I just wish that Bards could use martial weapons" as opposed to a feature that fits the concept.
However, I could see adding Whip.
transcendantviewer wrote:
In that case I'd make it two-handed martial weapons, not just any martial weapons.
How's this for a capstone ability: You can hit an opponent with your instrument and do a stupid amount of damage, but it destroys your instrument. You also have to take a long rest to recover before you can do this again.
That's a fair point, but for the sake of avoiding silly rules debates, it's better to just write it a bit differently. I've seen players try their damnedest to rules-lawyer their way into some stupid combinations.
"The Lore and Valor uses of Bardic Inspiration dice are guaranteed to have their effect occur."
This is not really true. First bards can't even use their own inspiration dice, second they can't use it to raise their spell dc or limit the saves of enemies. They can give an ally the ability to add to an attack roll, save or skill. Lore bards can reduce enemies hit, ability check, or damage. None of this makes any of their spells easier to cast or harder to resist. The lvl 3 ability seems a bit much for me, I would probably just use cutting words, and reflavor as a dread effect, that way you know it is balanced.
Bump. I have no more ideas for this thread, but I keep hoping to see it grow....
Elfcrusher wrote:
How about if Cacophony were a sustained spell (meaning, you could keep it up for as long as a minute, but you can't do anything else, and subject to Concentration checks) that, while active, imposes Disadvantage on all rolls by all hostiles within 30' who fail their saves? (New save every round) Maybe more fun/interesting/different than adding flat damage bonus. Usable 1/long rest or something.