Bloodcast (Whenever this deals damage, the next spell you cast this turn costs less for each point of damage dealt.)
CascadeRecruit [N?] (Whenever this attacks an opponent, exile cards from the top of your library until you exile a creature card [that costs less]/[that costs N or less]/[with less power]/[with N or less power]. You may put it onto the battlefield tapped and attacking that opponent. Put the exiled cards on the bottom in a random order.)
RebelRecruit N - (Whenever this attacks an opponent, you may pay . If you do, exile cards from the top of your library until you exile a creature card [that costs N or less]/[with N or less power]. You may put it onto the battlefield tapped and attacking that opponent. Put the exiled cards on the bottom in a random order.)
KaaliaRecruit N (Whenever this attacks an opponent, you may put a creature card from your hand with power/CMC N or less onto the battlefield tapped and attacking that opponent.)
Another totally off-the-wall thing, if we want to play up the Valhalla-esque aspects of Nordic flavor and/or make this more a shard of undead (which is feasible if you in turn make Neter more ruled by spiritual undead and make Valheim home to the physical ones):
Battleraise (During combat, you may cast this from your graveyard. [If you do, you may have it enter the battlefield tapped and attacking.] Battleraise only one card per turn.)
I was going for something like a hand-based Transfigure. Perhaps, taking a page from Transmute...
Mutate GUB (GUB, Discard this card: Search your library for a creature card with the same converted mana cost and cast it without paying its mana cost. Shuffle your library afterwards.)
My issues with this are:
1) I think anything that involves recycling from the graveyard should more properly go in Neter. Essya's not really about reuse, as much as it is about adaptation and predation. Grave-cycling-type things tend to indicate slow, relentless stagnation, which is the part of Neter that Essya disagrees with.
2) If Essya's a place of biological, mutating diversity, anything that encourages tribal play should be discouraged.
What if we do a Mental Magic-style mechanic?
Evolving Luk 2G
Creature - Plant
Mutate 3G (You may cast this spell for its mutate cost. If you do, when it enters the battlefield, it's sacrificed and you may search your library for a creature card with the same converted mana cost and put it onto the battlefield. Shuffle your library afterwards.)
3/2
Legendary Creature - Human Angel Knight
Flying, vigilance, haste, exalted
Whenever a creature you control attacks alone, all damage that would be dealt to it this turn is dealt to target creature instead.
5/4
Next: Riku of Two Reflections and Sisters of Stone Death (THAT'S some interesting fan fiction right there)
Magea, the Bleak Prophet XWB
Legendary Creature - Human Mystic
Magea, the Bleak Prophet enters the battlefield with X +1/+1 counters on it.
T: Put a +1/+1 counter on Magea. You gain 1 life.
T, Remove a +1/+1 counter from Magea: Put a +1/+1 counter on each other creature you control. Each player loses 1 life.
0/0
Next: Olivia Voldaren and Val Kish, Blood Arbiter
Eliza's Rage XUBR
Sorcery
Eliza's Rage deals X damage to target creature or player. That creature can't be regenerated this turn. When the creature dies this turn, you may return a creature card from your graveyard to your hand.
I'm actually okay with that. Or a version that uses -1/-1 counters, if you want something more toxic.
Regarding the descendency mechanics, I actually think they're a better fit for Neter than for Essya, at least phrased that way--W has a greater appreciation for the past and tradition than U. But that's just me.
Essya's U would, IMO, slant its BG away from its cycle-of-life-and-death-obsession-with-the-past side, and more towards its adaptability and focus on self-improvement. Less graveyard tricks, more +1/+1 counters.
What about a Modular variant?
Adapt N (This enters the battlefield with N +1/+1 counters on it. When it dies, you may put its +1/+1 counters on target creature.)
And then we treat Essya's creature menagerie like a cross between the Arcbound creatures and Shadowmoor/Eventide's counters-matter creatures.
Graveswarm 1BRG
Sorcery
Exile all cards from target player's graveyard, then choose one or both--Target creature gets +1/+0 until end of turn for each card exiled this way; and/or Graveswarm deals damage to target creature equal to the number of cards exiled this way.
Shatterblood Licid 1RW
Creature - Licid
1:symrw:, T: Quickening Licid loses this ability and becomes an Aura enchantment with enchant creature. Attach it to target creature. You may pay to end this effect.
:symrw:: Shatterblood Licid or enchanted creature gets +1/-1 and gains first strike until end of turn.
When Shatterblood Licid or enchanted creature dies, it deals damage equal to its power to each player and each creature.
1/1
Devourer Luk 1GU
Creature - Plant Vampire
ToggleLegacy - Whenever Devourer Luk deals combat damage to a player, if there are at least four creature cards in graveyards, that player puts the top three cards of his or her library into his or her graveyard.
2/2
1) More difficult to teach to new players, but this has been gone over already.
2) The fact that the physical design of the cards makes them immune to things like Ixidron for no particular in-game reason. If morph shenanigans work on changelings, nameless races, and even other werewolves from different planes, why should Innistrad's werewolves (and possessed little girls, and Jekyll/Hyde scholars, and angry mobs, and lab-wrecking lizard monsters, and shapeshifting vampires, etc) be any different? It's a pet peeve, yes, but one that does irk me, albeit irrationally.
Bit too defensive for Valheim, IMO.
I like Battleflash, but still kind of prefer Bloodthirst.
More Neter, for me. I think Essya, given the presence of blue, wouldn't want to set up game states where it wins through stagnant endurance.
Bit too parasitic for me.
In general I'm not exactly a fan of reanimation mechanics for Essya, if only because the flavor seems against undead at the moment.
I can see nothing wrong with this, but I don't love it. Not sure why, ignore me.
Nice, but I kind of want something meaner.
DeadlyImprove N (Whenever this deals lethal damage, put N +1/+1 counter/s on it.)
SneakyImprove N (At end of turn, if [a card]/[at least N cards] was/were put into graveyards from anywhere, put N +1/+1 counters on this.)
I like.
Kind of a more limited Haunt. Not that I necessarily mind, but it seems to fit more for Neter, IMO, even name-wise.
My two cents:
Adapt/Mutate - Whenever <trigger condition>, put N +1/+1 counters on this creature.
(Short response is short; am also working on schoolwork ATM.)
What if it's a counter-matters shard, backed up by a counter-giving mechanic? What matters isn't your original strength, but how much you were able to mutate and improve over others.
(For Neter: I think counter-matters is more Essya than Neter. If we're going for Neter not being a graveyard shard, my best solutions would be either life-matters, which is, as stated, difficult to balance, or perhaps something to do with the exiled zone, flavored as the spiritual afterlife? Or maybe even "sacrifice matters," specifically, although that brings it close to Jund. Tokens?)