Necromancer

Necromancers are a special class that has a focus on raising undead to fight for them. These undead, zombies or skeletons, are not strong by themselves but can be a threat once they gather. The undead they raise do not stay after an arc is finished. This means that necromancer starts an arc of weak until they find an opportunity to raise some.

The undead group themselves can be used in multiple ways. They add free damage while they are alive, so keeping them that way is good. At the same time, they can also be used as disposable creatures that can be used to hold off a powerful enemy to buy yourself team to heal or retreat. They are also pretty hard to fully kill off, but keep them away from multi-hit attacks and AoE holy damage.

Raise Undead can be used either during combat to get a group going, or you can chain cast it once a combat is over. Soulreap combines the raising of the undead with a heavy attack, allowing you to build up your forces without wasting AP or letting you get two active in 1 turn, provided there's already a corpse somewhere.

Corpse Explosion uses your raised undead as a resource. It is a powerful aoe for the cost which can be further empowered by using more corpses. This trades long term fight potential for a quick gain and it may not be worth blowing too many zombies on if you can't restock afterwards.

Corpse Domination lets you raise an enemy you killed to help you in the fight. It's not worth using unless it's on a heroic target, but adding another body to the battlefield on your side can swing the battle in your favor. It's powerful in fights against multiple heroic enemies.

Speak with dead is an out of combat utility ability. The usefulness on it depends heavily on the situation, as well as the GM.

One last thing to keep in mind as a necromancer player is that most people are not fond of zombies and skeletons. If you stroll into town with a small undead army behind you, don't expect a warm welcome in most places.