Diablo III is still going strong even five years after its release, and Blizzard is bringing an all new character type soon. The Necromancer is currently being tested in a live environment via an invite-only beta that opened yesterday. Those who have opted in to Diablo III beta testing might be included in the test, but spaces are limited. Just check your email to see if you got invited and you can go from there. Blizzard has warned multiple times however that the beta is extremely limited, so unfortunately you can't get your hopes up.
For those of us left on the outside looking in, we know that once the beta is concluded, Necromancers will be available to all of those who own and play the game. The beta testing will have hopefully smoothed over any issues so those of us playing afterward get the best experience.
What we have to look forward to is a character that commands via “blood, bone, curses, and hordes of obedient minions,” according to Blizzard. Necromancers will be able to summon various bone attacks to fend off their enemies. Blood based spells will steal life from those that seek to defeat you. There are scythes that you can summon to annihilate your foes. And you can reanimate the dead to do your bidding. This is just a small sampling of what will be available to players when Necromancers are added officially into Diablo III.
Keep your eyes on the beta test, as those included in it are sure to be sharing videos and screenshots of the action. Once the beta has concluded, the full release is sure to follow.
Source: Battle.net I & II