Druid/Necro combo, need help with what 3rd rl friend should be

[Tetrian]

Mage or enchanter.

Personally i would pick the mage for a trio like that - Mage adds that extra bit of petting and damage that enables you to take down almost anything.

Enchanter is very viable too. and its a nice and fun class - especially if you wanna group alot, but if its a pure a trio like that, the necro already have the CC handled in most cases with FD pulling.