Card sounds may differ from in-game as they get updated.
Aegis - Aegis protects a unit or player from one enemy spell or effect. It doesn't block friendly effects, nor does it stop battle damage from Killer attacks, Relic Weapons, or normal attack and blocking.
Ambush - An ambush unit can be played at the end of the enemy player's turn, or any time they are attacking you. If you played against a Killer or Relic Weapon attack, an Ambush unit will jump in the way to block that attack.
Flying - Flying units can only be blocked by other flying units, but can block ground units normally. They can also be directly attacked by Killer units and Relic Weapons.