[AreaOfEffect]

There are several forms of shapechanging and each type follows slightly different rules.

The Black Sorcerers of Machaka
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These shapeshifters have no control over their ability to change form. Not either as a battle command or as a command on the map view. These units only change when their hit points fall to zero. There new form will always have more hit points and they will retain the damage they have taken from their old form, but no more damage then they had in hit points before. These rules also apply to units like the Skinshifters of Vanhiem and the Jaguar Warriors of Mictlan, yet they are followers and not leaders, so you wouldn't be able to control their shapeshifting anyhow. At the end of combat, all of these units will revert to their previous form.

The Dai Oni and Oni Generals of Yomi
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These units act roughly the same as the Black Sorcerers above accept that their new form is actually weaker in hit points. In this case the damage from their previous form is wiped away. This difference makes the mechanics behind their transformation completely different. However, in practice the results are much the same except in cases where the unit has regeneration. The unit will revert to its old form after combat if it lives.

The Dragon Pretender Chassis
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These units have two forms from which they cycle through, like the others above, but unlike the others, you can control which form they start in before combat. You can also issue commands in combat to change form as well. Here it becomes important as to which form your in before combat. Dragons in human form act like Black Sorcerers. They will revert to a tougher form if brought to zero hit points and keep some damage. If they shapechange because of a command, they will revert back to their pre-combat form after the battle. If a dragon shapechanges because of damage, they will remain in dragon form after the battle. The damage transformation takes precedence. If the dragon is in dragon form at the start of combat, it will not transform but simply die.

The Skatti of Niefelheim
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This is one of those rare cases where the unit has three forms: a middle health form (Sorcerer), a high health form (Werewolf), and a low health form (Wolf). This unit is using the same mechanics as the dragon pretender, but with a twist. The result is that things get weird when you shapechange in battle because the mechanics were designed originally for units with two forms. If you use the shapechange command in combat, the unit will shapechange again after combat. If you use the shapechange commad multiple time in combat, it will shapechange after combat for the same number of times as it did while in combat. This means that if you shapechange once, it will shapechange once again. Since the progression is not binary, you will end up in wolf form if you started the battle in sorcerer form and changed once. You will end up in sorcerer form if you started the battle in wolf form and changed twice. Change form three times in combat to end up where you started after combat. Tests show that you turn into a werewolf if you are taken to zero hit points in either sorcerer or wolf form. You will not transform if you start in werewolf form and instead you will simply be dead. At the end of combat, if you shapeshifted from damage, you should remain in werewolf form.

This is NOT a comprehensive list of shapeshifting. Though I hope you appreciate the information. Let me know if you want a rant about the particularities of Machaka's Black Hunters or Sauromatia's Androphag.