basically they spam their spirts and cause the teams to kill the spirts first ... if they don't kill the spirts they get attacked by them ... the popular ones are .... every hit blinds u and every hit interrupts u ... pretty good if u ask me
I saw a full ritualist team one time. They ran a terrible terrible build combined with spirit spammers and restoration healers. The channelers were using the item lines such as caretakers charge and renewing surge... both of which have bad damage output when the big thing in HA is spike spike SPIKE.
I have seen teams with between four and six necro primarys being quite sucessfull in halls, 1 or 2 with rit secondary basicly spamming the spirits which on top of their usual effects keep the teams energy nicely topped up due to high soul reaping.