(fields marked with a * are open to suggestions)
Icon: A "Broken Note" (of the sort that is usually associated with bad singing in comics/cartoons)
Associated Colour: Pale Silver?
Appearance: A slight "echo" effect around the head of the effected player or monster.
Effects: Decreases attack speed (NOT attack animation speed like Stun does, you attack at normal speed but it increases the delay between swipes/shots), increases charge times and reduces turn speed (and possibly reduce block effectiveness, but that might make it too OP.)
Trap: The Sonic Trap would be a large speaker built into the floor.
Sonic Enemies*:
Noisy Puppy: A Gun Puppy with a Speaker/Microphone/Amplifier in it's mouth.
Kacophonous Kat: A Kat that can inflict Sonic.
Sonic Devilite*: A Silver Devilite with an MP3 player & Headphones that throws music discs.
Sonic Slime*: A Slime that, if effected by Sonic, emits small AoE pulses at regular intervals, resembles a less shiny and slightly see-through Quicksilver.
Sonic Polyp*: A Sonic Polyp, has an appearance similar to the slime above.
Silver Greaver: A Sonic Greaver
Sonic Howlitzer*: A Sonic Howlitzer
Restless Dead: A Sonic zombie that has a "Scream" attack instead of the "Breath" attack Zombies normally have.
Howler & Alpha Howler: Wolvers that can inflict Sonic.
Soundbot: A Sonic Scuttlebot
Sound Knight: A Sonic Mecha Knight
Silver Shankle & Screaming Wisp: Shankles/Wisps that can inflict Sonic.
Sonic Weapons & Armour*:
The weapons would deal either Normal or Elemental damage, and the armour would defend against these as well.
Soundmaster Series (Sword):
Appearance: An Axe resembling a guitar
Normal Attack: Basic 3 hit combo, slightly slower than weapons with a similar combo (i.e. Leviathan Blade) but has a chance of inflicting Sonic on attack.
Charged Attack: Strums the weapon like a Guitar, creating an AoE shockwave that damages and knocks back nearby enemies.
Names (from 2-star to 5-star):
Soundmaster, Advanced Soundmaster, Super Soundmaster, Soundmaster 5000
Sonic Cannon Series (Gun):
Appearance*: ???
Normal Attack: Fires a beam of concentrated sound, below average damage and fire speed but a large mag and near-instant projectiles.
Charged Attack*: ???
Names (from 2-star to 5-star):
Sonic Cannon, Amplified Sonic Cannon, Cacophony Blaster, Decibreaker
Soundwave Series (Bomb):
Appearance: A Large speaker with a Battery and/or Amplifier attached to the back.
Attack: Essentially a Haze Bomb that inflicts Sonic.
Names (from 2-star to 5-star):
Soundwave, Amplified Soundwave, Cacophony Generator, Sonic Boom
(I'll try and think up the Armour & Shield later)