Raging Grassquatch glitch? Need drop for HM LMB

[Kyriyas]

For the HM LMB skill... the fog mushroom that drops from the Raging Grassquatch is resetting on me when it gets to around 23% health.  Is there a mechanic I'm missing?

[Kyriyas]

Got my answer on Discord. You can buy fog mushrooms from the peach vendor in Celestial Basin. 

[Noalaa]

,,,and from the achievement vendor in Zeiwei