The Rift Tome

At the beginning of your End Step put a Chapter counter on The Rift Tome.
{t}: Add X Mana of any colour where X is
the number of Chapter counters on The Rift
Tome, Activate only if you control a Horror
Creature
Sacrifice The Rift Tome: Proliferate X times,
where X is the Number of Chapter counters on
The Rift Tome.