As a non-native speaker I have a doubt, because some cards do not use "as attacker/defender" wording.

Question is: can I use cards like Green Hatchling or Feigned retreat when I'm the attacker? I think not, but I'm not sure.

Feigned retreat can be used both when you are the attacker and when you are the defender. Since it does not specifically say attacker or defender you can use it in both instances.

For Green Hatchling, it says that it gains an intrigue icon in challenges initiated against you. Whenever you are attacking, you are actually initiating the challenge so he does not get an intrigue icon. So I guess he only gains an intrigue icon when you are the defender only.

I don't know exactly what happens in melee when, for example, somebody redirects a challenge and you are the target of the redirect. I guess he won't gain an icon then since the challenge wasn't initiated against you? (not sure )

Rogue30 said:

They end up not being the same thing.

Feigned Retreat says "when an opponent would win a MIL challenge against you...". The phrase "win against" indicates that you can be the attacker or defender, so long as you are losing. Said another way, the word "win" does not carry a distinction for which side (attacking or defending) you are on.

Green Hatchling says "...during INT challenges initiated against you." The phrase "initiated against" indicates that you must be the actual defending player because the only way a challenge can be initiated against you is if someone is specifically attacking you. Said another way, "initiated" carries the distinction of a player on the defending side of a challenge.

In Melee, "against you" only counts if you are the actual defending player. So if Player A attacks Player B with an INT challenge, Player C's Hatchling does not gain the icon. Also, challenges redirected through Crown Regent are considered to have been initiated against the new defending player. Challenges where someone "pitches in" to defend through the "Supports" mechanic of titles are not. So the Green Hatchling will gain the INT icon if you find yourself defending because of Crown Regent, but will not if you decide to help another player that you Support.