Starting from depth 11, some monsters appear as mutated. The mutations are:
- Explosive: 0.5× HP, 0.5× defense, explodes on death. (Summons orange glow like an explosive bloat) Forbidden for waterborne monsters.
- Infested: 0.5× HP, 0.5× defense, releases creeping death (LICHENS) when dies.
- Agile: 2× move speed, 1.5× defense, blinks, flees on low HP. (Act as wraith and imp mixed)
- Juggernaut: 3× HP, 0.5× move speed, 0.5× attack speed, 0.75× defense. Forbidden for monsters that maintain distance. (Berserk as a slow-moving ogre or a quick result on a hasted goblin – casted by a goblin totem)
- Grappling: 1.5× HP, 0.5× defense, seizes his prey on attack. Like a bog monsters, forbidden for them, and krakens.
- Vampiric: Has transference. Forbidden for monsters that maintain distance. Similar to the vampire, and disappears while summoning bats.
- Toxic: 0.5× attack speed, simultaneously saps strength (like centipede) and poisons (like spider).
- Reflective: Reflects ½ spells; ¼ are reflected back to caster. Forbidden for spellcasters (as they are already hard to reach).
Additionally, a mutation is forbidden for a monster that already has at least one of newly acquired abilities. Imps cannot be agile because they already blink, golems cannot be reflective, because thay alreay reflect, and so on.
Polymorphing a monster will also remove its mutation.
Negating a mutated monster will remove any extra abilities added from the mutation. This includes the explosion on death from explosive, the creeping death from infested, the blinking from agile, the seizing from grappling, the transference from vampiric, both effects from toxic, and the reflection from reflective. The sidebar and the monster's description may still mention the mutation but these will be inaccurate.
The following table gives the chance for a monster generated on a given depth to be mutated. All possible mutations are equally likely.
| Depth | % Chance |
|---|---|
| 11 | 1 |
| 12 | 2 |
| 13 | 3 |
| 14 | 4 |
| 15 | 5 |
| 16 | 6 |
| 17 | 7 |
| 18 | 8 |
| 19 | 9 |
| 20-26 | 10 |
| 27 | 11 |
| 28 | 13 |
| 29 | 16 |
| 30 | 18 |
| 31 | 21 |
| 32 | 25 |
| 33 | 30 |
| 34 | 35 |
| 35 | 41 |
| 36 | 48 |
| 37 | 56 |
| 38 | 65 |
| 39 | 75 |
| 40 | 75 |