Follow the melee close and get into the thick of things using spirit walk. Then begin.
Mass confusion - Some enemies will no longer threaten you or your allies(without you having to kill them) and will hopefully do some damage
Haunt - get this going too keep up your mana as the fight prolongs.
Toads and more Confusion - Confusion has no mana cost and with the rune has a 4s cooldown(what?). Keep casting it and use toads for the kind of chaotic damage only a witch doctor would appreciate.
Save horrify for when this build sucks and you just need to gtfo.
And of course I couldnt help but be reminded of Annie when i saw the gargatuan glyph.
p.s. Forgot to mention. Dont foget to run around picking up globes.