Dark Ritual

What is Dark Ritual?
Dark ritual is a new tab that opens under the 'UPGRADE' main tab, after the player has completed area 3-4 (Dank Dining Hall)

The player can use gold to buy workers, which they can then assign to certain rituals, indicated by the gem icons below the worker section. The more workers assigned to a ritual, the faster the ritual completes (indicated by a % counter on the gem tooltip, and by the 'colour' of the ritual gem filling up).

Each ritual provides a unique bonus to stats, or resource caps.

Whilst Dark Ritual itself stays unlocked after rebirth and reincarnation, as do the ritual benefits, any workers purchased are reset.

Workers
Workers are bought using the buy button on the Dark Ritual screen, with gold. The cost increases per worker bought.

Worker Cost Formula - $$100*1.05^x$$ ($$100*1.05^x$$ in web versions, 1.4.4.0 or older) where X is equal to the number of workers you currently have.

Ritual time
Time to fill a gem is equal to $$Base Time*Multiplier^{level}$$ before reduction multipliers are applied. Each assigned worked contributes $$1*WorkerSpeed$$ every second.

Purchases and Upgrades
Slime Bank

Yunanjian Monster Taming - Increases worker efficiency by x% per every 100 captures you have in total. Total captures can be found on the tooltip. X is increased per upgrade of this.

Spirit Upgrades

Enchanted Gem Clock- Reduces ritual time (time to fill gem) by x% per lvl capping at needing only 0.852% of the time at max (lvl 50)

Note
As of 1.4.8.1, the proficiency gem is the only one waranting an active hunt for the boss core (assuming you have reincarnation skills). Others either do too little to matter or (HP, MP regeneration) get a significant effect only when you already should farm the bosses for other reasons.