Wizards within 6" of these haunted forests or gardens are able to channel two additional dice if they have ANY spells from the lore of death, undeath, vamps,or nekehera. This can obviously be double nasty for WD slaans or lore of death slaans as they will be channelling up to 5 dice on a possible 5+. Missed it the first time, but it also says when channeling "power dice." Still pretty nasty in my opinion.
Or just a High lore Slann. pretty easy to switch out a spell for a Death spell, and pretty useful too, because that lore have some fairly potent spells. I find it pretty awesome that our Slanns benefit so much from this