| Maw demon | 1 | Fiend (demon) | Medium | 13 | 33 | | chaotic evil | | Volo's Guide to Monsters | | | | | | |
| Maurezhi | 7 | Fiend (demon) | Medium | 15 | 88 | | chaotic evil | | Mordenkainen's Tome of Foes | | | | | | |
| Mastiff | 0.12 | Beast | Medium | 12 | 5 | | unaligned | | Monster Manual (SRD) | 13 | 14 | 12 | 3 | 12 | 7 |
| Master thief | 5 | Humanoid (any race) | Medium | 16 | 84 | | any alignment | | Volo's Guide to Monsters | | | | | | |
| Master of souls | 4 | Humanoid (human) | Medium | 12 | 45 | | neutral evil | | Adventures (Descent into Avernus) | | | | | | |
| Marut | 25 | Construct (inevitable) | Large | 22 | 432 | fly | lawful neutral | | Mordenkainen's Tome of Foes | | | | | | |
| Martial arts adept | 3 | Humanoid (any race) | Medium | 16 | 60 | | any alignment | | Volo's Guide to Monsters | | | | | | |
| Marilith | 16 | Fiend (demon) | Large | 18 | 189 | | chaotic evil | | Monster Manual (SRD) | 18 | 20 | 20 | 18 | 16 | 20 |
| Marid | 11 | Elemental | Large | 17 | 229 | fly, swim | chaotic neutral | | Monster Manual | | | | | | |
| Mantrap | 1 | Plant | Large | 12 | 45 | | unaligned | | Adventures (Tomb of Annihilation) | | | | | | |
| Manticore | 3 | Monstrosity | Large | 14 | 68 | fly | lawful evil | | Monster Manual (SRD) | 17 | 16 | 17 | 7 | 12 | 8 |
| Manshoon | 13 | Humanoid (human) | Medium | 19 | 126 | | lawful evil | | Adventures (Dragon Heist) | | | | | | |
| Manes | 0.12 | Fiend (demon) | Small | 9 | 9 | | chaotic evil | | Monster Manual | | | | | | |
| Mammoth | 6 | Beast | Huge | 13 | 126 | | unaligned | | Monster Manual (SRD) | 24 | 9 | 21 | 3 | 11 | 6 |
| Male steeder | 0.25 | Monstrosity | Medium | 12 | 13 | | unaligned | | Mordenkainen's Tome of Foes | | | | | | |
| Magmin | 0.5 | Elemental | Small | 14 | 9 | | chaotic neutral | | Monster Manual (SRD) | 7 | 15 | 12 | 8 | 11 | 10 |
| Magma mephit | 0.5 | Elemental | Small | 11 | 22 | fly | neutral evil | | Monster Manual (SRD) | 8 | 12 | 12 | 7 | 10 | 10 |
| Mage | 6 | Humanoid (any race) | Medium | 12 | 40 | | any alignment | | Monster Manual (SRD) | 9 | 14 | 11 | 17 | 12 | 11 |
| Lizardfolk shaman | 2 | Humanoid (lizardfolk) | Medium | 13 | 27 | swim | neutral | | Monster Manual (BR) | 15 | 10 | 13 | 10 | 15 | 8 |
| Lizardfolk | 0.5 | Humanoid (lizardfolk) | Medium | 15 | 22 | swim | neutral | | Monster Manual (SRD) | 15 | 10 | 13 | 7 | 12 | 7 |
| Lizard king queen | 4 | Humanoid (lizardfolk) | Medium | 15 | 78 | swim | chaotic evil | | Monster Manual (BR) | 17 | 12 | 15 | 11 | 11 | 15 |
| Lizard | 0 | Beast | Tiny | 10 | 2 | | unaligned | | Monster Manual (SRD) | 2 | 11 | 10 | 1 | 8 | 3 |
| Lion | 1 | Beast | Large | 12 | 26 | | unaligned | | Monster Manual (SRD) | 17 | 15 | 13 | 3 | 12 | 8 |
| Lich | 21 | Undead | Medium | 17 | 135 | | any evil alignment | Legendary | Monster Manual (SRD) | 11 | 16 | 16 | 20 | 14 | 16 |
| Leviathan | 20 | Elemental | Gargantuan | 17 | 328 | swim | neutral | | Mordenkainen's Tome of Foes | | | | | | |