Tell me if I get this.
Turn 1: Attack 1 -> Creature Attacks, deals 1 dmg -> End turn -> Attack goes up to 2.
Turn2: Invert Attack -> -2 -> Creature Attacks, deals -2 dmg -> End turn -> Attack goes to -3.
Turn3: Invert Attack -> 3 -> Creature Attacks, deals 3 dmg -> End turn -> Attack goes up to 4.
Turn4: Invert Attack -> -4 -> Creature Attacks, deals -4 dmg -> End turn -> Attack goes to -5.
'Cause if this is the case, after 10 turns the creature would have dealt a whooping -5 dmg.
Also, what happens when you AM it?