This spell costs {X} less to cast, where X is the total mana value of Auras you control

Enchant creature

Enchanted creature has flying and gets +1/+1 for each life you have. (For example, if you have 8 life, it gets +8/+8.)

When Invincible Mantle is put into a graveyard from the stack or the battlefield, exile it. If you do, return all enchantment cards from your graveyard to the battlefield.