MTG Salvation

As has already been said, Chaotic Mind is mostly a one-sided Teferi's Puzzle Box, a card that's not tearing up any formats. I think it would actually be more acceptable if it affected all players, making everyone play Red's game and messing up a control opponent's carefully constructed hand. Unlike the puzzle box, this card could then deck your opponent because of the discard, but at the same time they're getting access to the same accelerated card flow that you are so I think it would be alright. 2RR seems right.

I could maybe see this getting printed without the may ability, so that you are forced to move your counters onto whatever enters the battlefield, friend or foe. It feels more like an out of control contagion that way, and gives your opponent an out to waste a bunch of counters on a 1/1.

Spellbreaker 1W
Creature - Human Cleric
Purge (creatures lose all abilities while blocking or blocked by this)
2/2

It hoses keywords like Deathtouch, First strike, Trample, Lifelink, activated abilities, and 'when this dies' triggers. It only lasts during combat, so cretures can use their magic again after attacking if they survive.

Just don't put any characteristic defining abilities like Tarmogoyf's into the set to avoid that confusion.

The second batch looks quite good. The gold counter cards seem to 'easy' for White-- White is so far from ramp/colorfixing that giving it Repeatable (Taxman) and Free (Earned Reward) gold at common feels wrong. Here's how I would do them:

Taxman 2W
Creature
When ~ enters the battlefield, if target opponent controls more lands than you, you gain a gold counter.
2/2

The taxman now catches you up for a turn if you're behind or playing second. I worry that on-curve now it's a bit weak. If you can afford the power, 1W 2/2 or 2W 2/3 could be considered.

Buy Off W
Instant
Prevent all damage target creature would deal this turn. It's controller gains a gold counter.

or

Swords to Pickaxes 1W
Instant
Destroy target attacking creature. It's controller gains a gold counter.


Lock & Load looks like it does good things for the set, but I'm not exactly clear on how it works. Can you cast the exiled card as much as you want this turn, or only once? If the former, I think you could use a shorter wording: Lock & Load (Exile this as it resolves. You may cast it from exile this turn.) If the latter, I think you would need to tack on 'If you cast this from your hand...' to the beginning of the ability.

Here's the best way I can think of to implement it, by letting you tutor it from your sideboard at any time. I originally had you exile it from your deck at the start of the game, but with that version you could play with 20 Conjure cards and a 40-card deck, which wasn't ideal. I could see some neat uses for a mechanic like this.

Conjure COST (If this is outside the game, you may pay COST to put this in your hand instead of drawing a card.)

I like where you've gone now with the Spirit Tether ability. Before I got that far, I thought of another way to represent splitting a creature's body and soul upon death:

Kind of like Mausoleum Guard 3W
Creature - Human
Dualism (This enters the battlefield with a +1/+1 counter on it. If it would die, you may remove a +1/+1 counter from it instead. If you do, remove all damage from this and put a 1/1 spirit creature token with flying onto the battlefield.)
1/1

This is a (wordy) idea I've had for awhile on building structures. You invest your creatures' time to get a more powerful ability.

Golem Factory 4
Artifact
Build - Tap an untapped creature you control: Put a charge counter on ~. Activate this ability only on your turn.
8, T: Put a 4/4 Golem Artifact Creature onto the battlefield. This ability costs 1 less to activate for each charge counter on ~.

This mechanic reminds me of one of the design challenges from the first Great Designer Search. Part of the challenge was to design another card in this cycle of cards with a doubled effect:
Really Focus (uncommon) 4U
Sorcery
Discard any number of cards, then draw that many cards.
Then, discard any number of cards, then draw that many cards.

You might find something useful in the cards and comments there to help you design interesting Double cards at higher rarities. Of your cards, I especially like Swift Expansion. Ramp cards are generally undesirable late game, but in an environment with Double, you can discard Swift Expansion to amp up another Double card. These kinds of effects that have different value early and late game are particularly nice candidates for Double.

I think that Gestating Visions would be more straightforward as an Enchantment, a smaller Centaur Glade

Saproling Bed G
Enchantment [C]
3G: Put a 1/1 Green Saproling Creature token onto the battlefield.

In isolation I like the themes of this mini-set a lot. I am guessing that there are five of these mini-sets, one for each 4-color combo, and that they are meant to be played/drafted together as part of a single big set. In that context, the preponderance of Allies makes sense to me. But in that context, I don't see enough support for 4-color specifically. Shaman's totem, for example, is five-color fixing, at which point you might as well play five color instead of 4-color. Strong linear themes in each 4-color chunk (like Allies) will help with that, but I think you should also consider making your fixing 4-color.

The cleanest way rules-wise may be to change these into enchantments you can use for a spell effect with Evoke. Late late game you can use the effect on multiple turns, or early game you can cash it in for a single turn's use.

Rune of Lightning 6R
Enchantment
2R: ~ deals 3 damage to target creature.
Evoke R (You may cast this for its evoke cost. If you do, it's sacrificed when it enters the battlefield.)

I like Peek a lot. Each Peek card by itself gives you a chance at a bonus, and when you combine it with library manipulation or other Peek cards you get to feel clever. There are two things that I think you should pay attention to with the mechanic.

First, as pointed out already, having multiple Peek cards each with its own 'if you peeked at a [CARD TYPE], [EFFECT] trigger requires you to remember too much between turns. You have to remember the order in which you return your Peeked-at cards at end of turn, and then stack your attack triggers on your next turn to make sure you match up the card types and effects. That would be demanding with physical cards, but sounds like an absolute nightmare with something like Magic Online. I highly recommend the group-reveal tech that Astrolabe suggested:

Peek Bear 2G
Creature - Bear (C)
Peek (Whenever this creature attacks, exile the top card of your library. Return it to the top at the beginning of the next end step.)
~ gets +1/+1 as long as you Peeked at a Creature card this turn.
2/2

Peek Caster 3R
Creature - Wizard (U)
Peek (Whenever this creature attacks, exile the top card of your library. Return it to the top at the beginning of the next end step.)
You may cast Instant and Sorcery spells you are Peeking at.
3/1

Second, I can see some potential feel-bad moments with Peek as an attack trigger. I'm taking a big risk if I attack Peek Bear into a 2/3-- If I hit with my Peek I'm fine, but if I miss I just chump-attacked. I do like how tying Peek to attacking makes you commit for it, but you could consider making it "Peek (at the beginning of combat on your turn, exile the top card...)" instead. I prefer the gameplay of your current Peek, but it's something to think about.

The current version of Ruin would be most palatable to me in a set either with a high amount of Artifacts, or Morph, or some other mechanic that lets your opponent keep casting some of their cards if all they have are Deserts.

Another direction is to make more cards that Ruin only your own lands and not your opponents. This would complement the Dune-matters cards you hinted at, and reduce how often Ruin is used to randomly color-screw an opponent.

I've been experimenting with Absorb in a Cowboys and Aliens set as a force-field mechanic for the aliens. I'm generally using it on X/1s, which makes them very weak to -1/-1 effects but resistant to repeated damage. Absorb also interacts well against deathtouch, lifelink, infect/wither, and combos great with the ability to block multiple creatures. It's a mechanic that should be used sparingly though, and as such I think it works best to give identity to a faction. I would use it on cards a little less frequently than a Guild or Clan mechanic.

This is a nice looking batch and should lead to some cohesive strategies in draft. I like that Resurrect is self-limiting. If it still gets out of hand, you could try changing the cost to discarding a land instead of sacrificing one, as in Retrace.

The green/blue mechanic is a little weird. I'm using a similarly flavored green/blue mechanic in one of my sets that generally plays a little simpler (but still has some rules complexity):
Mutate Bear 1G
Creature
Mutate (Whenever you cast a creature spell, you may have this become a copy of that creature until end of turn.)
2/2