It really has to be built in this order for the build to work, otherwise i highly recommend trying it out
Archmage's Gem
PASSIVE - Every 0.5s you gain a stack of Demise, causing your next damaging ability that hits an enemy god deals an additional 1.5% of your Magical Power in damage and remove all stacks. This effect stacks up to 20 times.
Y10 Evolved Warlock's Staff
Y10 Soul Gem
PASSIVE - On successful hit of an Ability you gain 1 stack. At 3 Stacks your next Ability that damages an enemy God will deal bonus damage equal to 20% of your Magical power to each God hit, and will heal yourself and allies within 20 units for 15 (+5 Per Level) and will consume the 3 stacks.
Y10 Book of Thoth
PASSIVE - You permanently gain 7 Mana per Stack, and receive 5 Stacks for a god kill and 1 Stack for a minion kill (max. 75 Stacks). You gain Magical Power equal to 4% of your Mana from items. At 75 stacks this item Evolves, gaining 10 Magical Penetration and Increasing the Magical Power gained from Mana to 7%.
Soul Reaver
PASSIVE - Your abilities deal an additional 1% of the target's maximum Health as Magical Damage. If the target has over 2000 Health, your ability bonus damage scales up. This effect reaches a maximum of 9% Maximum Health damage at 2750 Health. Subsequent hits on the same target do half the bonus damage for the next 3s.