-Flame Imp: Even on first-turn this card takes 3 damage to you. It's too much a risk to put in the deck if you don't get it first turn it's a hindrance. 1 mana crystal for a SLIGHTLY better minion but it does 3 damage to you.
Suggestion: Just make the damage 1-2 if you have to, otherwise replace battlecry.
-Pit lord: 2 mana crystals less than Lord of the Arena, yet does 5 damage to you without a taunt. Not worth it in the slightest. IF warlocks could heal themselves like priest/paladin, maybe, but otherwise there isn't a point in using it.(too much cost for minimal gains).
Suggestion: Really I'd only suggest 1-2 damage if that.
Twisting Nether: While I do like the idea, the cost is a bit high. Mages can easily output more damage with spell power and a lot less cost. Rogues can return to hand with 6, and to be honest it's just an underwhelming card. It's 50/50 dice-roll if your opponent has any cards in his hand.
Suggestion: Raise to 9-10 or keep at 8, but make it only enemy cards.