I wrote a
poison creeper druid guide for v. 1.09 in which I wrote
Energy -- Your goal here is to arrive at over 500 mana. (Over 600 mana is even better.) If you can do this without placing any points in energy then go for it. If you are unable to attain this amount of mana using only equipment than you might place as much as 35 points into energy. Usually this amount of mana is fully adequate for all your summoning and casting needs. There are a few battles, however, during which you will need to drink a potion. Fighting Lister and his gang in hell comes to mind.
I stopped playing at v. 1.09 so I don't know if my advice holds true for later patches. The poison creeper druid is a variant build--not cookie cutter--and I am very proud of it.
