Units come in classes. Classes determine unit abilities and limitations. Known classes include:
There are classes of special significance:
Unit Stats and Abilities
Statistics are numerical values that are used by the Combat, Magic, or other systems of the Erfworld universe. Generally, the higher the number is, the better the Unit is. As these values increase, power increases linearly. 
- Move - Distance a Unit can move during its Turn
- Hits - Amount of damage a Unit can take before croaking
- Combat - Offensive combat value. Sometimes referred to as Attack.
- Defense - Defensive combat value.
Units also have some hidden statistics:
- Loyalty - how strongly a Unit is aligned with its RulerErf-b1-p084a
- Experience - How far a Unit has progressed towards gaining its next Level. Experience is (usually) gained by croaking enemies.
Units may also have one or more Natural (or Special) Abilities.
Some units have abilities that can achieve unconventional results, and can be used when not on Turn. These abilities are named Natural AbilitiesErf-b1-p040a and are sometimes referred to as Special Abilities.
|FlightErf-b1-p040a||Flying units can Move through the air without falling.|
|Water||Water units can Move through the water without drowning.Erf-b1-p060|
|ForestErf-b1-p062||Forest units can attack in forests.|
|Dance FightingErf-b1-p127||Dance fighting units sing and dance while fighting.Erf-b1-p111|
|Light||Light units can enter tunnels.Erf-b1-p098a|
|SiegeErf-b1-p046a||The ability to breach walls.Erf-b1-p126|
|Mount||Can be ridden by humanoid units|
|HealingErf-b1-p022||Unit can heal wounded allied Units|
|FabricationErf-b1-p040a||Allows a Unit to create Coins and other items, is a form of natural Dollamancy.|
|LeadershipErf-b1-p040a||A Unit with Leadership:|
|CasterErf-b1-p084a|| A Caster:
Royal and Noble Units
It's possible free will is a innate trait to Royals, as most of the non-Ruler royals are described as ornery and contrary to their progenitor's wishes.
- Engineer-class infantry
Some units types don't have classes, but do have descriptors and may have multiple forms, like Golems.
Garrison units may have special classes in addition to their basic class.
- Tunnel Capable (Spidew/Sourmander) - A Heavy Unit capable of entering tunnels
- Tunnel Fighter (Gobwin/Marbit) - Provides a bonus at fighting in tunnels (These could be the same Ability, applied to Heavy and Light Units respectively.)
- Breath Weapon - Allows the Unit to use a short/medium range "breath" attack before or instead of melee.
- ArmoredErf-b1-p077 - Probably increases the Unit's Defence. Armor may also be Equipment instead of an ability.
Regeneration may be preventable by fire damage, or simply an incredibly overwhelming amount of damage. Both were dealt to Bogroll and he did not regenerate.
Possibly the Regeneration mechanic is that any sub-lethal damage is healed very rapidly, but that any attack powerful enough to kill the unit will not be regenerated. There have been two twolls damaged in Erfworld book one, most notably Bogroll, but also a twoll apparently killed in one blow by Jillian (page 10 frame 5). This is only pertinent if all (or at least most) twolls regenerate, of course.