| Leucrotta | 3 | Monstrosity | Large | 14 | 67 | | chaotic evil | | Volo's Guide to Monsters | | | | | | |
| Lemure | 0 | Fiend (devil) | Medium | 7 | 13 | | lawful evil | | Monster Manual (SRD) | 10 | 5 | 11 | 1 | 11 | 3 |
| Lamia | 4 | Monstrosity | Large | 13 | 97 | | chaotic evil | | Monster Manual (SRD) | 16 | 13 | 15 | 14 | 15 | 16 |
| Laeral silverhand | 17 | Humanoid (human) | Medium | 18 | 228 | | chaotic good | | Adventures (Dragon Heist) | 13 | 17 | 20 | 20 | 20 | 19 |
| Kuo toa whip | 1 | Humanoid (kuo-toa) | Medium | 11 | 65 | swim | neutral evil | | Monster Manual (BR) | 14 | 10 | 14 | 12 | 14 | 11 |
| Kuo toa archpriest | 6 | Humanoid (kuo-toa) | Medium | 13 | 97 | swim | neutral evil | | Monster Manual (BR) | 16 | 14 | 16 | 13 | 16 | 14 |
| Kuo toa | 0.25 | Humanoid (kuo-toa) | Medium | 13 | 18 | swim | neutral evil | | Monster Manual (BR) | 13 | 10 | 11 | 11 | 10 | 8 |
| Kruthik hive lord | 5 | Monstrosity | Large | 20 | 102 | | unaligned | | Mordenkainen's Tome of Foes | | | | | | |
| Kraken priest | 5 | Humanoid (any race) | Medium | 10 | 75 | swim | any evil alignment | | Volo's Guide to Monsters | | | | | | |
| Kraken | 23 | Monstrosity (titan) | Gargantuan | 18 | 472 | swim | chaotic evil | Legendary | Monster Manual (SRD) | 30 | 11 | 25 | 22 | 18 | 20 |
| Korred | 7 | Fey | Small | 17 | 102 | | chaotic neutral | | Volo's Guide to Monsters | | | | | | |
| Kobold scale sorcerer | 1 | Humanoid (kobold) | Small | 15 | 27 | | lawful evil | | Volo's Guide to Monsters | | | | | | |
| Kobold inventor | 0.25 | Humanoid (kobold) | Small | 12 | 13 | | lawful evil | | Volo's Guide to Monsters | 7 | 15 | 12 | 8 | 7 | 8 |
| Kobold dragonshield | 1 | Humanoid (kobold) | Small | 15 | 44 | | lawful evil | | Volo's Guide to Monsters | | | | | | |
| Kobold | 0.12 | Humanoid (kobold) | Small | 12 | 5 | | lawful evil | | Monster Manual (SRD) | 7 | 15 | 9 | 8 | 7 | 8 |
| Knight | 3 | Humanoid (any race) | Medium | 18 | 52 | | any alignment | | Monster Manual (SRD) | 16 | 11 | 14 | 11 | 11 | 15 |
| Killer whale | 3 | Beast | Huge | 12 | 90 | swim | unaligned | | Monster Manual (SRD) | 19 | 10 | 13 | 3 | 12 | 7 |
| Ki rin | 12 | Celestial | Huge | 20 | 152 | fly | lawful good | Legendary | Volo's Guide to Monsters | | | | | | |
| Kenku | 0.25 | Humanoid (kenku) | Medium | 13 | 13 | | chaotic neutral | | Monster Manual (BR) | 10 | 16 | 10 | 11 | 10 | 10 |
| Kamadan | 4 | Monstrosity | Large | 13 | 67 | | unaligned | | Adventures (Tomb of Annihilation) | | | | | | |
| Juiblex | 23 | Fiend (demon) | Huge | 18 | 350 | | chaotic evil | | Mordenkainen's Tome of Foes | | | | | | |
| Jarlaxle baenre | 15 | Humanoid (elf) | Medium | 24 | 123 | | chaotic neutral | | Adventures (Dragon Heist) | | | | | | |
| Jaculi | 0.5 | Beast | Large | 14 | 16 | | unaligned | | Adventures (Tomb of Annihilation) | | | | | | |
| Jackalwere | 0.5 | Humanoid (shapechanger) | Medium | 12 | 18 | | chaotic evil | | Monster Manual (BR) | 11 | 15 | 11 | 13 | 11 | 10 |
| Jackal | 0 | Beast | Small | 12 | 3 | | unaligned | | Monster Manual (SRD) | 8 | 15 | 11 | 3 | 12 | 6 |