RED answered your questions very poorly.
To answer the first one, the Healing Enhancement would be Negated if you tried to play it during the Battle Phase, since FbtN Negates all Characters and Enhancements (not just in battle). However, if you wait until the Discard Phase, you can safely heal then so long as Darius' Decree is not active and you have a Hero of matching Brigade to play it on.
To answer your second question, set-asides can be Negated. If you attack with Moses and are blocked by The Strong Demon, you may not play Feast of Booths to withdraw from battle. However, as long as Darius' Decree is not active, you can play a set-aside on Moses or any of your other Heroes while Moses is in play during Prep or Discard phase as Special Abilities on Characters are only active while they are in battle. RED is correct in that abilities gained by Set-Aside Cannot be Negated, so if you play Gathering of Angels on The Strong Angel (during Prep or Discard phases), when he returns he does not Negate his own gained banding ability.
