RE: Disco mastery abilities.
You can select the damage type using the context menu on the Bard Mastery book
So make sure you choose the right damage type.
Typically I'll hunt in shame against the non-casting mobs and crank out Despair on them after discording them. (The strength reduction from Despair stack on top of discord effect)
You can run both disco and tribulation at the same time, but thats a huge mana crunch.
Tribulation I use mostly in group fights, vs high end mobs. If i go out with a couple of sampires or paladins, and drop tribulation on a mob, it can proc off of both of their swings.
Base Despair damage from a 4x bard with slayer instrument is 180 dmg per round. Tribulation proc will increase that to 315