College of Metal

You are one of the few and proud inducted into the prestigious College of Metal, founded by Sabbath The Black. A strange breed of Bards, the members of this college are known for their love of loud music and raucous, near-violent parties which often involve a strange form of dance-combat; a style copied by their more enthusiastic fans. They wade ecstatically into war, being able to strike hard against their foes or empower their allies with their music. The flames of the Abyss in their tongues, the horns of Valhalla in their songs, the spirit of demons and the undead in their hearts; they are like roiling thunder crashing through the battlefield with booming voice and cacophonous performance.

Bonus Proficiencies

When you join the College of Metal at 3rd level, you gain proficiency with medium armor and the greataxe, greatsword, halberd and maul. You also gain proficiency with the Performance skill. If you are already proficient in Performance, you gain expertise instead.

Back in Black

At 3rd level, your intimacy with jarring noises has granted you resistance to Thunder damage. Albeit this is not without cost, as the prolonged exposure to such sounds has left your hearing weakened. You have disadvantage have on perception checks which rely on hearing, as well as disadvantage against saving throws for any effect that leaves you Deafened.

Additionally, your passion for chaos is so intense that it imbues your very life force. The size of your hit die is now equal to your bardic inspiration die.

At 17th level, your resistance to Thunder becomes immunity instead.

Immigrant Song

Starting at 3rd level, you can use your cacophonous melodies to disorient your enemies. You can now choose to grant your bardic inspiration to a hostile creature. Said creature can't roll the die. Instead, whenever it saves against an effect imposed on it by you, you may roll the die and subtract the result from the creature's save.

Dance of Eternity

At 6th level, you learn the Shocking Grasp cantrip, and it doesn't count against your number of bard cantrips known.

You also become proficient in a new type of instrument of your design, which is powered by the lightning you generate. This item seems to be an electric Guitar (or any other electric instrument), and is called a Heavy Instrument. When played normally it sounds like a normal bass guitar, but you can cast Shocking Grasp targeting the guitar as a bonus action (no attack roll required) to make it sound like an electric guitar until you stop playing. For the crafting of this instrument, you must use a Heavy Martial melee weapon you own as the base, as well as invest 4 hours, and 100gp worth of materials.

The Heavy Instrument functions as the weapon you used for the base, as well as a spellcasting focus for your bard spells. While playing it as an electric guitar, you may increase the save DC of your bard spells by a number equal to half of your proficiency bonus (rounded down).

Twilight of the Thunder God

Starting at 6th level, you can strike twice, instead of once, whenever you take the Attack action on your turn, but only if you use your Heavy Instrument for both the attacks. When you attack with your Heavy Instrument, you can use your Charisma modifier, instead of Strength or Dexterity, for the attack and damage rolls. You may also change the damage type of your attacks with the instrument to thunder.

With your improved instrument in hand, you have become even better at jarring your enemies with your music. If a creature fails a saving throw against one of your bard spells as a result of rolling your bardic inspiration die, it gains vulnerability to Thunder damage till the end of your next turn. If it was resistant to thunder, it instead has no resistance instead.

Psychosocial

At 14th level, your finesse in sowing discord has transcended materiality. As an action, you can let loose a scream targeting the very minds of your enemies. Target a number of creatures upto your proficiency bonus within 60ft of you. 

Each target must make an Intelligence saving throw against your spell save dc. On a failed save, a target takes 14d6 thunder damage and is stunned. On a successful save, a target takes half as much damage and isn’t stunned. If a target is killed by this damage, its head explodes, assuming it has one.

A stunned target can make an Intelligence saving throw at the end of each of its turns. On a successful save, the stunning effect ends.

Once you use this feature, you can't do so again until you finish a long rest.