So I’m thinking about tempting my party with a grimoire of death magic at some point. If they choose to use it an not destroy it, how would I handle them being able to raise reanimates and such? I know the spells can be stylized however they need to be to feel right, but I’m unsure of exactly how to handle it.

Perhaps the book is the equivalent of a magic tome, but the benefits it provides are:

When using this tome with the Conjure spell the Additional Summon and Summon Ally effects are added without increasing the difficulty. Additionally, each turn you may perform one Concentrate manoeuvre as an Incidental to maintain a Conjure Spell. Creatures summoned with this tome will always be undead or ghostly in nature.

It’s a powerful book, it does more than most implements in the system, but obviously has its downside, if it got into the wrong hands it could spell disaster.

Also if the players don’t fully understand what the tome is then perhaps don’t tell them that last sentence of the description, keep that for when they use it and you get to describe the rotting corpses and skeletal forms clawing up out of the ground!