I farm PvP with
+2 purple +1 red -1 yellow
Fill either Dark Maiden or Hellcat first (aim for red / purple / green match, considering your banner and mana links)
Use Hellcat, Dark Maiden or Sekhma's spell only if this will give you an extra turn *
Use Hellcat only on (best to worst)
Use Dark Maiden only on (best to worse)
Blue (if Sekhma is already filled and this will allow Sekhma cast to get an extra turn)
Use Behemoth whenever available and if you can't use any other spell.
With Sekhma, aim for your main concerns. (ex : Mab, Famine, Gorgotha, Kerberos). He should rapidly be able to two shot them.
*: the main concern for this team is frozen. Sometimes you'll have to go out of the "aim for extra turn" strategy for a fast kill on Mab by sniping her with Sekhma
Note : Behemoth is more than expendable AND arguably on par with Ice Golem as a frontliner for this team.
Note 2 : Be aware that most of the time, you will fire Sekhma on blue gems lining up with skulls, as you continuously remove yellows with Dark Maiden, but that's more than OK. The occasionnal extra turn from Brown / Yellow are very appreciable though.