| Yan c bin | 18 | Elemental | Huge | 22 | 283 | fly | neutral evil | | Adventures (Princes of the Apocalypse) | | | | | | |
| Yeenoghu | 24 | Fiend (demon) | Huge | 20 | 333 | | chaotic evil | | Mordenkainen's Tome of Foes | | | | | | |
| Yellow musk creeper | 2 | Plant | Medium | 6 | 60 | | unaligned | | Adventures (Tomb of Annihilation) | | | | | | |
| Yellow musk zombie | 0.25 | Undead | Medium | 9 | 33 | | unaligned | | Adventures (Tomb of Annihilation) | | | | | | |
| Yeth hound | 4 | Fey | Large | 14 | 51 | fly | neutral evil | | Volo's Guide to Monsters | | | | | | |
| Yeti | 3 | Monstrosity | Large | 12 | 51 | | chaotic evil | | Monster Manual (SRD) | 18 | 13 | 16 | 8 | 12 | 7 |
| Yochlol | 10 | Fiend (demon, shapechanger) | Medium | 15 | 136 | | chaotic evil | | Monster Manual | | | | | | |
| Young black dragon | 7 | Dragon | Large | 18 | 127 | fly, swim | chaotic evil | | Monster Manual (SRD) | 19 | 14 | 17 | 12 | 11 | 15 |
| Young blue dragon | 9 | Dragon | Large | 18 | 152 | fly | lawful evil | | Monster Manual (SRD) | 21 | 10 | 19 | 14 | 13 | 17 |
| Young brass dragon | 6 | Dragon | Large | 17 | 110 | fly | chaotic good | | Monster Manual (SRD) | 19 | 10 | 17 | 12 | 11 | 15 |
| Young bronze dragon | 8 | Dragon | Large | 18 | 142 | fly, swim | lawful good | | Monster Manual (SRD) | 21 | 10 | 19 | 14 | 13 | 17 |
| Young copper dragon | 7 | Dragon | Large | 17 | 119 | fly | chaotic good | | Monster Manual (SRD) | 19 | 12 | 17 | 16 | 13 | 15 |
| Young gold dragon | 10 | Dragon | Large | 18 | 178 | fly, swim | lawful good | | Monster Manual (SRD) | 23 | 14 | 21 | 16 | 13 | 20 |
| Young green dragon | 8 | Dragon | Large | 18 | 136 | fly, swim | lawful evil | | Monster Manual (SRD) | 19 | 12 | 17 | 16 | 13 | 15 |
| Young kruthik | 0.12 | Monstrosity | Small | 16 | 9 | | unaligned | | Mordenkainen's Tome of Foes | | | | | | |
| Young red dragon | 10 | Dragon | Large | 18 | 178 | fly | chaotic evil | | Monster Manual (SRD) | 23 | 10 | 21 | 14 | 11 | 19 |
| Young red shadow dragon | 13 | Dragon | Large | 18 | 178 | fly | chaotic evil | | Monster Manual | | | | | | |
| Young remorhaz | 5 | Monstrosity | Large | 14 | 93 | | unaligned | | Monster Manual | | | | | | |
| Young silver dragon | 9 | Dragon | Large | 18 | 168 | fly | lawful good | | Monster Manual (SRD) | 23 | 10 | 21 | 14 | 11 | 19 |
| Young white dragon | 6 | Dragon | Large | 17 | 133 | fly, swim | chaotic evil | | Monster Manual (SRD) | 18 | 10 | 18 | 6 | 11 | 12 |
| Yuan ti abomination | 7 | Monstrosity (shapechanger, yuan-ti) | Large | 15 | 127 | | neutral evil | | Monster Manual (BR) | 19 | 16 | 17 | 17 | 15 | 18 |
| Yuan ti anathema | 12 | Monstrosity (shapechanger, yuan-ti) | Huge | 16 | 189 | swim | neutral evil | | Volo's Guide to Monsters | | | | | | |
| Yuan ti broodguard | 2 | Humanoid (yuan-ti) | Medium | 14 | 45 | | neutral evil | | Volo's Guide to Monsters | | | | | | |
| Yuan ti malison | 3 | Monstrosity (shapechanger, yuan-ti) | Medium | 12 | 66 | | neutral evil | | Monster Manual (BR) | 16 | 14 | 13 | 14 | 12 | 16 |
| Yuan ti mind whisperer | 4 | Monstrosity (shapechanger, yuan-ti) | Medium | 14 | 71 | | neutral evil | | Volo's Guide to Monsters | | | | | | |