"Hell's Horns, History of he Hellhorned," by Grrrg Onehorn. The terrible handwriting of the imp scribes has made this tome an excruciating read and something I don't plan on returning to soon.
Multistrike is an extremely potent status effect on units that have high Damage output. The fragile effect can be pretty devastating to units, thus it is advised to use Onehorn's Tome on units that have already Damage Shield or Armor on them. Keep in mind that with more strikes comes greater danger from Spikes as well.
Emberstone is very good on Onehorn's Tome if you do not have Ember generation that allows you to play it with high cost.
Removing consume from Onehorn's Tome can be extremely potent. The fragile effect is no additional downside on a unit that already has fragile and thus stacking more and more multistrike is very strong.
Stackstone is very potent on Onehorn's Tome as this means, you will get two additional strikes out of a single spell cast. Keep in mind that the Ember increase needs to be prepared for.