Spec used: Beastmaster / Pet used: Spirit Beast / Gear level: 480 (mostly PVP).
Must have talents: Exhiliration, A Murder of Crows, Barrage.
Glyphs: Marked for Death, No escape, Endless Wrath.
Start the fight by using Concussive Shot on Dark Summoner. Once the first shadow is up, pop Bestial Wrath and the trinkets (optional) and nuke the shadow. The pet will be on the shadow, obviously.
Return to Dark Summoner, pop all the left cooldowns, Stampede, A Murder of Crows, Serpent Sting. If you notice that Dark Summoner is attacking your pet, switch fast on the second Shadow with all the rest of the pets from Stampede.
Keep going
Return again to Dark Summoner. After this, you need to kill the other shadow mobs. You can leave your pet on Dark Summoner and only use Kill Command when you have enough aggro with the shadow.
Use Ice Trap on shadow / Dark Summoner, when is not on cooldown. Use Exhilaration when your pet is very low on health. You have two exhilarations and one Heart of the Phoenix.
Last tip. Use feign death if your pet is dead, you already have used Heart of the Phoenix and Dark Summoner has more than 20% hp. You will reset the fight and save gold from repairs.