Target Priority is what determines where the game AI attacks with enemies and during auto battle. What determines Target Priority, or "Aggro" as it is sometimes called is unknown; however an understanding of Aggro is important when deciding who to give your last health pot to, or who you want your knight to defend next turn.
While the basis for target priority is very vague, research suggests that the following things will raise or lower a hero's target priority.
Things that raise target priority: (Roughly in order of importance)
- Higher power/evolution/level
- Lack of resistance to the damage type the hero is attacking with
- Certain abilities can trigger an increase in aggro, like Capture
- Low max hp
- high damage output
Oddly, characters with low health do not seem to trigger any more aggro than they did at max health.
Things that lower target priority: (Roughly in order of importance)
- Low level
- Low damage output
- High resistance to the damage type the hero is attacking with