does Ethon's ability stack with Mangler? (Attack: Attack 1 ship. When attacking, you may change 1 of your HIT results to a Crit result.)

(When an enemy ship inside your firing arc at Range 1-3 is defending, the attacker may change 1 of its Hit results to a Crit result.}

as in the ability to turn TWO hits to crits? and does his ability work on himself?

Yes to everything.

1. Yes - you can even stack Calculation or Mercenary co-pilot on top to get 3 crits

2. Yes - note that the card does not say anything along the lines of "when another friendly ship is attacking a ship within your firing arc" - the triggering conditions are: enemy ship is defending, enemy ship is within Etahn's firing arc - provided those conditions are met, his ability triggers.

Thanks.. Thought that was the case but just wanted to be sure...