Dark Ritual is one of the five Alpha boons. It was potentially the second best of the boons (after Ancestral Recall), operating as two-thirds of a Black Lotus for mono-black decks. It was removed from core sets after 5th Edition as designers felt it hurt in the design of black cards (the ritual ability it represents has been shifted from black to red). Remnants of Dark Ritual's influence remain with cards that add mana at worse rates, encouraging playing more black spells to take advantage of it, such as Liturgy of Blood, Priest of the Forgotten Gods, or Dark Petition.
Interestingly, Dark Ritual has seen somewhat frequent reprint in recent years in special deck sets that do not affect format legality and which are aimed at the casual player, in Duel Decks: Divine vs. Demonic, Planechase, Duel Decks: Phyrexia vs. The Coalition and From the Vault: Twenty.
Dark Ritual is also notable for being printed with a variety of outdated card types (and the most different card types any one card has had), being at different points an interrupt and a mana source before becoming an instant.