For the first phase, start with a slash to bait a charge, then use the whirlwind and do 6 basic attacks (or 3 spin attacks), walk away from him, re-use whirlwind and perform again 6 basic attacks (or 3 spin attacks).
For the second phase, line up the blastworms like in the video, hit stagnox 6 times with normal attacks then attack the two blastworms individually, this will damage stagnox enough for him to die in 1 cycle.

Note 1: for second phase if you fail the quick kill knock down stagnox again then just hit him with 2-3 spin attacks, this will always guarantee a 2 cycle fight.

Last updated 08/24/2021 – Stovent