I don't understeand the warlock
Some of these negative effects can be mitigated, or made to use for your own benefit. The health loss from Life Tap or a Flame Imp for example can help you trigger the lower cost of Molten Giant (a large minion that has reduced life based on how much health your Hero has). Alternatively you could use a minion like Earthen Ring Farseer or a spell like Soul Siphon in order to heal that damage later.
Of course, the final alternative is to simply avoid those cards which have harmful effects, and focus on those that are purely positive, like Mortal Coil, Shadowbolt, Void Walker, etc.
I hope this helps you understand, if you have further questions, feel free to ask, I or some others I'm sure will try to answer them as best they can.
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