MTG Salvation

Currently, green doesn't deal direct damage to players nor planeswalkers. I could easily see Spirit Arrow as:

Choose one:
Target creature deals damage to target creature equal to its power.
Target creature deals damage to target flying creature equal to double its power.

I like the idea of a spell like this.

Disenchanter's Ring is totally fine. Aetherchoke would be fine, but not at this rate. Burning Aether could also be too cheap for its effect. I don't like Surging Greed. Colorpiewise it's okay, but it feels wrong to make such a card, as it PROMOTES playing artifacts and enchantments (If I play more of them, and I get targeted by this spell, maybe I won't have to lose life!). It's better against a deck that doesn't have artifact or enchantments. Voracious Edict is just a color pie break, so you'd probably need to find something else for Black.

It is nearly exactly Chandra's Ignition, but not hitting players and (probably) sacrificing the chosen creature. Notice that the creature doesn't die until State Based Actions checks are done after resolving the spell.

Sure, that is technically a green card. You could also give the creature deathtouch, because why not? It's green, right?
I don't think so. As it needs a creature, it's not as bad as Ezuri's Predation, probably (however it may be a sweeper for bigger creatures as well, potentially), but it still is a green sweeper. I like the color pie, I don't want it to become a grey goo. Please keep your creature sweepers out of green.

However...
I think something that makes the creature fight until it dies would be totally fine. Something like:
Target creature gets "0: Fight another target creature" until end of turn.
This could be OP. Indestructible creatures would be the worst offender, making it a Death Wind. Maybe it needs to be:
Target creature loses indestructible and gets "0: Fight another target creature" until end of turn.
This still leaves some OP cases, but it becomes just a better Lure.

No. At least not like this looks right now, as Armaggedon would just win you the game. How about:
"Whenever a spell or ability you control either counters a spell or ability an opponent controls, destroys one or more lands an opponent controls or causes an opponent to discard one or more cards, draw a card."
"Either" is not used normally, but helps understand the sentence.
I COULD understand rewarding such hideous behavior as land destruction , but the card you proposed seems to me to be just busted, having it be very easy to conserve card advantage before you Armaggedon and still have a lot of mana to close the game. It was too broad and too powerful in what it was doing, if you ask me. This version is much less explosive, yet more powerful in a long game filled with counterspells and Sinkholes. It's also shorter.

I don't see what is the interaction of new version with fetches. They have activated abilities. More of a problem is probably neither intended nor necessary, landfall hate.

As you noticed, like this, it is DOA. You can change "when enters target " to "as enters" to mitigate it. 0/0 and */* is the same in this way.
I feel that a card should not combine exile with exile until leaves. It's going to be hard to remember which card is which. "nonland permanent cards " seems needlessly complicated. Also,counting all cards in exile in a oblivion_ring.dck (as it looks like you try to create it) would be cumbersome and very prone to missing some cards (blinks, orings of other players). Is it worth it?

They have a rule now that no land can be strictly superior to basic. Being Legendary is not enough drawback, as the first one in deck is always superior to basic.

Quite a neat idea, but I have some general feedback:
The cycle isn't in WUBRG nor WBGUR (consecutive enemies) order. It would be more elegant if this was possible.
I wonder which one is more appropriate colorpiewise on blue creature: "Sacrifice (specific) red creature: do blue thing" or "Sacrifice (specific) red creature: do red thing". I think both are ok, but I'm not sure.

I assume this (a rule) is a triggered ability. Who is its controller, and where does it go on stack if there are other at the beginning of upkeep triggers?

How do you imagine commenting this card, that OBVIOUSLY panders to CCI, without discussing it? If you wanted an Ugin card in any other format than EDH to play with morph, you could and should leave it colorless, as an Ugin card should be. Having a color on an Ugin card is a blasphemy in my book.
Having 6 power and toughness for 6 mana is not a minimal effect, especially that it doesn't demand any color.
How do you imagine mana base building with this card? A lot of sources of different colors, to be able to flip it, and a lot of colorless sources to use the emblem? I get that it creates colorless mana itself, but this is really awkward.
Having a planeswalker that can sweep a majority of board AND stay on 4 loyalty to do it again is a lot, probably too much.
I feel like second +1 should be rather instead something like "-5: Draw three, manifest any number", or even "-9: Draw seven, manifest any number". Like this, this card lacks a Timmy factor, that should be easily supplied in a card like this. Also, "+1:Draw two, protect myself" seems to be to easy to run away with a game. I don't think there was a planeswalker in this game that plused, made card advantage and board state in the same ability.

Well, this card is very weak, powerwise speaking. It's enough that you don't control a Conspiracy effect, and it self-sacrifices on ETB.
But seriously, try to match modern magicese (removed from the game? Really? What is it, 2005?) and think if the card even works as you want it to.

602.1. Activated abilities have a cost and an effect. They are written as “[Cost]: [Effect.] [Activation instructions (if any).]”
602.1a The activation cost is everything before the colon (:). An ability’s activation cost must be paid by the player who is activating it.

Maro said many times that they tried many times to use similar mechanic to this or land tokens instead of Evolving Wilds. It failed. The main reason is having to have something on you besides deck, trying to shuffle lands into library after game and (for tokens) inability to tap beads. Of course, some of those aren't problems in cube environment.
One card that uses this mechanic is Sovereign's Realm. It was designed so you can't have basic lands outside of those played by this, and it is in environment where there is no card asking about basic land type (Choke, Invigorate), so they can easily be reploaced by playing cards from your hand face down. Just a food for thought.

One with Nothing OP?
In what format, in what deck, you think that's ridiculously OP? I don't any major format would be broken by this card. (Any) Standard? Killed by any one mana remocal, and it doesn't enter before turn 2 at the soonest. Modern? You theoretically could push it to T1, but it would require a lot of deckbuilding, and I think you could do worse things than this. Legacy is similar. Vintage? Well, you could as well be dead on your T1, and this effect is still very mild looking at other possibilities you have in this format.

This card seems fair to me. It could be powerful in some aggresive black deck, but even at its best, when opponent discards from a full hand, opponent can leave his best card for later. I would be totally comfortable with this effect at four mana, on three it could be potentially too oppressive and swingy. Still, I think it should be a little more resilent, so it's not 3 mana One with Nothing so often. Maybe it should be 1/3?

What if the creature was dealt damage before, and you need only one damage to kill a 4/4?

I also would like to tell that I like your Niv Mizzet. It's a nice change to see a value, not combo Niv. I'd drop your/opponent's turn clause (leaving once per turn) to make it a little stronger and lower deck consturction requirements. I feel it's underpowered now.