Diablo – How much experience is required for each level

Once you start getting into the stronger spells, you will likely run into mana issues unless you have some sort of strategy for boosting mana. Otherwise, you'll have to pace yourself.

Acid cloud and Locust Swarm are two spells I use fairly frequently. If I open with Grasp of the Dead, then cast two Acid Clouds, I won't have enough mana for Locust Swarm.

It really depends on your build, though. Many pet-centric builds may not really require much in the way of mana assistance, since minions are "fire and forget" abilities.

The formula in question seems to be:

DR = Ak/(1+Ak) where A = armor, k = 1/(50*moblevel)

So, for example, at level 5, with 100 armor, fighting level 5 mobs,

100*.004/(1+[100*.004]), or .4/1.4, or roughly 28%.

Fighting level 10 mobs, this changes to

100*.002/(1+[100*.004]), or .2/1.2, or roughly 16%.

Thus, when you gain a level, without increasing your armor, the character sheets displayed damage reduction shrinks slightly, since 'equal level mobs' are better able to penetrate your armor. Among other things, this means that there's no DR involved here, Armor just keeps getting better, the more of it you have.