Underdark Monster CR ratings

Myconid CR 0,

Flumph CR 1/8,

Drow CR 1/4,
Grimlock CR 1/4,
Kuo-Tao CR 1/4,
Vegepygmy CR 1/4,

Chitine CR 1/2,
Deep Gnome (Svirfneblin) CR 1/2,
Myconid Adult CR 1/2,
Piercer CR 1/2,
Rust Monster CR 1/2,
Gazer (Beholder) CR 1/2,
Grey Ooze CR 1/2,

Duergar CR 1,
Kuo-toa Whip CR 1,
Quaggoth Spore servant CR 1,
Thorny CR 1,

Ettercap CR 2,
Grick CR 2,
Quaggoth CR 2,
Vegepygmy Chief CR 2,
Cave bear (or polar bear) CR 2,

Hook Horror CR 3,
Cave Fisher CR 3,
Choldrith CR 3,
Spectator CR 3,

Drow Elite Warrior CR 5,
Mindwitness CR 5,
Roper CR 5,
Umber hulk CR 5,
Troll CR 5,

Drider CR 6,
Kuo-Toa Archpriest CR 6,
Gauth (Beholder) CR 6,

Drow Mage CR 7,
Grick Alpha 7,
Mind Flayer CR 7,
Draegloth CR 7,

Drow Priestess of Lolth CR 8,
Fomorian CR 8,
Cloaker CR 8,
Spirit Naga CR 8,

Ulitharid CR 9,
Fire Giant CR 9,

Alhoon CR 10,
Death Kiss (Beholder) CR 10,
Abolet CR 10,

Morkoth CR 11,

Beholder CR 13,
Neothelid CR 13,

Elder Brain CR 14,
Death Tyrant CR14,

Purpleworm CR 15,

Shadow Dagons CR varies