Nephilim (singular: nephil; Hebrew) were powerful monstrosities with limited intelligence, that were venerated by the Cult of Yore, who saw them as the "Old Gods".   As such they were a symbol of the old Ravnica, before the time of the Guildpact. Unlike the created lords of the Guildpact, these entities did not make demands or accept sacrifices. They did not require or answer prayers. They were there only to humble; living, walking examples of the world's vastness, diversity, unpredictability, danger, wonder, horror, and complexity beyond comprehension. 
The Nephilim were subdued thousands of years before the events of the Ravnica block, and imprisoned deep below the plane's surface. Their precise origins are unknown. Once awakened by construction works in the Utvara district, five of the creatures fed on a dragon corpse and grew in size and power, showing a shared ability to absorb power from other beings. Almost forgotten for 10,000 years, the return of the Nephilim was seen as a sign for change and indeed it coincided with the fall of the Guildpact at the Decamillennial. Though they defeated Niv-Mizzet, he managed to destroy two of them. The remaining three made it to the center of Ravnica City where they were eventually subdued. Rakdos defeated one of them.
The five rare creatures of the cycle have different appearances; some are spirit-like, others beast-like. Each costs four mana of separate colors; the excluded color is the enemy color of the middle two colors.
- The name is taken from eponymous Hebrew biblical creatures. Nephilim is derived from the Hebrew נָפַל, "those who cause others to fall".
- The Nephilim were the first cards printed that needed exactly four different colors to play. None saw any tournament play, however, as their admittedly unique abilities were not seen to justify the difficulty of assembling those colors. 
- Dune-Brood Nephilim produces Sand creature tokens.
- Dissension had two cards referring to the Nephilim: the aura Blessing of the Nephilim and the instant Might of the Nephilim.
- Matt Cavotta. (February 22, 2006.) "Wake Up Call", Daily MTG, magicthegathering.com, Wizards of the Coast.
- Magic Arcana. (April 03, 2006.) "Guildpact Zoom-Ins", Daily MTG, magicthegathering.com, Wizards of the Coast.
- Mark Rosewater. (May 13, 2013.) "Absence", Daily MTG, magicthegathering.com, Wizards of the Coast.