Automatically reflect certain damage types (but become more vulnerable to others).
Chance to reflect ranged attacks.
Damage resistance increases with attacks taken, up to a limit (e.g. increases by 1% every time the unit is hit, up to 50% reduction). Kicks in when attacked but fades if more than X seconds go by without taking damage.
Damage resistance increases with damage taken (e.g. 90% health ->10% reduction, 50% health -> 50% reduction, max 90% reduction).