Below is a walkthrough for the Lyre and Brimstone side quest in Tiny Tina’s Wonderlands. To obtain this quest, interact with the help sign in the central eastern side of the area.
Talk to Sinistrella in the Weepwild Dankness
Follow the objective to Sinistrella in the northern part of the area near some vending machines and speak with Sinistrella.
Find the evil tree
Jump on the mushroom to the right of them and follow the path to reach the tree. Defeat the enemies.
Melee and collect 3 evil branches
Melee the tree and gather the branches that fall off.
Give evil wood to Talons of Boneflesh
Return to the band.
Turn off the speakers
Run to each of the 3 speakers while defeating the enemies that spawn.
Take spell recipe
Grab the spell.
Collect the Thoughts of a Tyrant, Craveness of a King and Vision of a Viscount
Make your way to the three objectives and defeat the enemies. Collect the items they drop then return to the band.
Put reagents in cauldron
Put the materials you collected into the cauldron then listen to the song.
Tell Talons of Boneflesh they win
Turn around and speak with Sinistrella.
Kill the Talons of Boneflesh
Defeat the band.
Talk to Zygaxis
Speak with the little Imp on the stage to complete the quest.