The basic combo is a mix of zero cost and full cost minions that equals chargers, Carnivorous Cube, Faceless Manipulator and Deathwing or Naturalize to fill your board with more chargers for lethal. Use Oaken Summons to complete your quest with Cursed Disciple and King Mukla. Emergency quest minions are Fatespinner, chargers and Faceless Manipulator. You really want to Ultimate Infestation AFTER Barnabus. Drawing up to five zer0-cost minions is game winning usually.
Your deck is very versatile for lethal, so don't always wait for an obvious combo. Check for different forms of lethal through buffs, chargers, deathrattles and/or drawing into it.
Always mulligan for Wild Growth, Oaken Summons, and if you have those cards you can think about Nourish, Wrath or Fatespinner according to your likelihood of needing ramp or a clear. For the Handlock or silly Shaman Shennanigans, you can use King Mukla and Naturalize to potentially mill their win condition, but I'd never advocate mulliganing for that. Never toss the quest.
Lesser Jasper Spellstone is your emergency killer of Carnivorous Cube or crowd control, but easily the worst card in the deck. Alexstrasza is a decent replacement for anything you are missing, as is Bonemare or a second Fatespinner. Avoid Branching Paths or Greedy Sprite or Ferocious Howl, they look okay, but they slow your gameplan down too much.