Necro suffers from long cast times on life taps and high mana cost. With the high level healing dot you have some flexibility but generally you will get nuked or meleed down before you get most spells off.
Another big problem is the wide usage of cure pots. You can cast half your mana bar on someone and they negate your effects with a few clicks of a potion. Its not cheap but at 60 you prolly have more cash on you then the cost of a click so it is worth it.
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