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So for raise dead it says you can make a new unit of zombies.... could you also add on to an old unit of zombies or do you have to use invocation for that?
Unless it says you can in the FAQ, then no. IoN must be used to heal raise into existing units.
Raise dead...description is clear, u RAISE new unit of zombies.
IoN...u cast it to restore wounds OR to give more models to an existing unit.
invo is better anyway D6+4 instead of D3+4 plus the casting value is lower