Change the SubCM set to CM and slash Taunt with Substitute.
Mention in the CM set that Substitute is useful for "scouting" and lowering Serperior's HP to Overgrow level.
Mention that Taunt helps prevent Pokemon from using Roar to phaze Serperior away, using Toxic, recovering, setting up, yada yada.
I'd switch around the slash of Life Orb and Leftovers. Life Orb really helps with the final damage output and Serperior can always Giga Drain HP back. It's also the superior item if you're using Taunt > Substitute.
Also put Taunt in dual screens somewhere.
After those changes, QC Approve 1/3