Great question!
In Mage Wars, the last event takes precedence. So, if you give your creature Eagle Wings after a Maim Wings, then it gains flying again.
This may be unlike some other games, where a negative effect takes precedence.
Mage Wars was designed to be intuitive and realistic. You can picture 2 Mages going back and forth, each struggling to get the last advantage. You cripple his Angel, destroying its wings so it can't fly. Then, he makes it sprout new Eagle Wings to fly!
Note: some conditions or enchantments may take away flying and prevent you from gaining flying while they are in place. In the above example, if in addition to Maim Wings the other player Restrains or Incapacitates your Angel (such a Lightning Bolt STUN condition), it loses and cannot gain Flying. So, the Eagle Wings still won't let it fly,even if it the last effect it receives. However, as soon as the STUN ends, then the Eagle Wings works, since it is the last effect.
I hope that makes sense!