A card from early lists that occasionally its way back in, the reasons being that the additional mana it provides generates enough mana to easily Burning Wish for Dark Petition to search for Ad Nauseam. Players often refer to it as additional copies of Lion’s Eye Diamond as it generates three mana, I try to not look at it that way as it takes careful planning with this deck to reach Threshold. Keep in mind that Lion’s Eye Diamond and Cabal Ritual have great synergy, if you have the mana readily available, cast your Burning Wish or Infernal Tutor, in response cast Cabal Ritual as it too is an instant and then hold priority and break Lion’s Eye Diamond to generate the Threshold required for Cabal Ritual.
I think my favorite thing about Cabal Ritual is it improves the quality of Past in Flames as a tertiary storm engine. What you can do is Burning Wish for Past in Flames, and then on the next turn use Infernal Tutor paired with Lion's Eye Diamond to find the Cabal Ritual. Cast Cabal Ritual and then flashback Past in Flames into an easy win.