Enchant creature
Identity- Enchanted creature deals lethal damage to another creature. (When a creature meets the condition, it gains Hunter's Prowess as an identity. When Hunter's Prowess becomes an identity, it is no longer considered a card and cannot be unattached and remains attached even when the enchanted creature changes zones).
Gain 4 life whenever the enchanted creature deals combat damage to a creature. If Hunter's Prowess is an identity of the enchanted creature, you may draw a card when the creature deals combat damage to another creature.
Today denizens of Multiverse, I present to you a new, born a search for mechanics that could be unique to auras.
Once a creature gains an identity, that identity lasts until the game ends. I added a clause to avoid dealing with "Destroy target enchantment" effects. Once a creature gains an identity, the identity becomes part of the creature (hence, the aura not being considered a card anymore), and its abilities are now part of that creature.
How do you know which copy of the creature has what identities when the creature is shuffled into the library? For physically-played Magic I have a simple solution that I believe to be elegant and is inspired by the check-cards for double-faced cards: a blank card. The blank card has the normal card backing that Magic: the Gathering cards have and has a blank front so that the player can write the name of the creature and its identities when the creature is shuffled into the library.
I would expect that other zones would not often have the same risk of not knowing whether a copy of the creature had gained any identities.
My greatest detraction of this proposed mechanic is that there's a lack innate usefulness the Identity mechanic- it's buildup that will rarely be relevant since the creature with the Identity is not guaranteed to come back from whichever zone it gets sent.
I use a more streamlined version on Words of Instinct. Maybe something to feed back into this idea?