That makes more sense. I think you wording can be clearer.
You and another target player each reveal the cards in their library. Each player chooses a nonland card from the other's library and Unrequired Feelings deals damage to each player equal to their chosen card then puts it into their hands.
You have to reveal the libraries to make them non hidden information, otherwise your opponent can 'fail to find' which goes against the spirit of the card, unless you wanted that as an option. I'm fairly certain I've got the wording right here but it could probably be done better.
The wording is a little messy, but its an interesting cards. Only real problem is you can't put cards owned by other players into your hand. You would need to be like Praetor's Grasp.
They look cool, Rashimi's second ability has a spelling error you put "rarget' instead of "target"
The current ability has the exile and choice of land as separate abilities so you exile first, these cards don't go into any particular pile as would happen with something like Ashiok, Nightmare Weaver. Then you look at any and all face up lands cards in exile and choose one of them regardless of who owns it or how it got into exile, Crumble to Dust, Delve for Dig Through Time, her own ability, and you can play that land. So long story short, yes you can hit previously exiled lands with her ability.
This Rashimi is much better, though the wording is atrocious. Try this.
-6: You get an emblem with "X: Exile target nonland permanent with converted mana cost X or less. Activate this ability only any time you could cast a sorcery." and "X: Cast target face-up noninstant, nonsorcery card in exile with converted mana cost X or less. Activate this ability only any time you could cast a sorcery."
This works perfectly fine. It doesn't have the brokenness of being any creature you run in your deck and doesn't screw you if you opponent has no creatures or simply doesn't want to play your game. It will have to cost in the 4-6 range as this is where we find this sort of effect nowadays. Though if you're just going for broken you can take Show and Tell and add a fight clause, though that seems to fly in the face of the flavor your shooting for.
The problem is that with that variant you opponent can essentially counter your spell by not putting a creature into play whether or not they have one in hand. Sure you get cool ETBs but it probably isn't worth. If you leave off the return and cost at least 5 it will be completely fair, the broken part of your first design was the tutor, if they need the card in their hands then it is much more reasonable.
A rather interesting story and thought procces for determining walker power level. My first thought on seeing Koth was omg that is bad, followed up with, damn he hit perfectly where he was trying(Tibalt power level). I like where Melira is right now, but she will only be powerful if there are enough counters in your set. Rashimi is interesting but her + is too powerful and an awkward fit in pie. It shouldn't put the land into play, she would have to cost at least 4 and probably be a - for that effect. So you can search to hand and drop the "If an opponent controls more lands than you" part and it fits right in pie and is pushing the power level. Her ultimate is strange and too weak. For a walker ultimate like that you want the cards to go into play or be cast, maybe one a turn from exile to play up her exiling. Most walker ultimate's should in theory read "win the game" because you are putting a lot of effort into getting there, unless you have a auto or 1 turn ult then you can scale it back to read "the game has shifted in your favor" Because she takes 3 turns to ult you want a more win the game feel, the trick is finding a unique way to do it and I think you have that, its just putting them into your hand makes it so you had to assemble some kind of combo that requires you to cast the cards and for them to all be the same.
Fair enough I suppose, though the story of Chandra has her at the head of an order of pyromancers, if I remember correctly, they are still active unless things have changed dramatically since BFZ. Totally possible with how things role in the magic world, but if pyromancers are being hunted down i would assume they are also fighting back. Hopefully we see some of that.
Completely different plane. Chandra was born on Kaladesh but the plane you are thinking of is Regatha, the one she fist walked to and has an order of fire monks. If we went to Regatha and found little to no fire magic most people would be upset.
If you can shift the majority of your designs to 'liking' your own color(s) as opposed to 'hating' your opponents color(s) you can avoid a lot of the issues brought up. But I mean a VAST MAJORITY like no more than a vertical cycle in each color of hate. The idea of having set 1 focus on helping single color then having set 2 being more modular in what colors you are is interesting but might be way too complex in practice. You might be able to compensate for this by having set 1 have 0 artifacts and set 2 has heavy(I'm thinking Mirrodin levels[or go simply colorless with prismatic for spells]) but with the prismatic mana to add colors to cards and effects. You can even have the prismatic mana show up mostly on abilities, having the ability change based on what mana is spent or being an ability that changes what color the permanent is. Overall I'm not sure how many interesting non confusingly complex/wordy cards you can get with prismatic so it might end up a small portion of your block but there are very interesting abilities you can do.
To demonstrate on with your Gleaming Plate as a reference
Gleaming Plate - 1SS
Artifact - Equipment (U)
Equipped has protection from the colors of Gleaming Plate.
Equipped creature gets +1/+3 if it shares a color with Gleaming Plate S: Gleaming Plate become the color of the mana spent to pay S. (S can be paid with one mana of any color.)
Equip 2
Addmitedly with this design there is little need for the actual S as it can easily be replaced with generic mana and simply spell out what needs to be done. Though if it ends up significant giving it its own symbol is a good way of showing that it is a mechanic
#1 seems to put too much burden on the caster considering its giving a benefit to both players. It might be fine but seems to encourge playing obsurd low drops as opposed to real cards(As in strictly combo as opposed to advantage creatures).
#2 has the exact same problem as the original only with a significant deck building restraint. "only run Blightsteel Colossus." Although now there is no longer that realistic option of your opponent being able to stop you with a random Fiend Hunter or Leonin Relic-Warder.
#3 Is by far the best for the intended effect of mimicking Guild Feud. It still combos into Blightsteel, but considering the other 1 was a one card combo turning this into a two card combo with Worldly Tutor is much better.
For Painful Dreams, there doesn't seem to be any reason for White in its cost. Also with such a drastic difference in the penalties it reads "Whenever a player plays a land if they have any cards in hand they loses 1 life." For something like this you either want both penalties to be equalish or make one obviously worse(as you have here) but make it so you will have to sometimes choose that one because the other choice is not possible. Something like "Whenever a land enters the battlefield its controller discards a card unless they sacrifice a creature." This way the price is rather significant on both ends but under a number of situations a player would change their choices through out the game. If you want it to be life payments a minimum of 2 is necessary for it to even feel like a choice with a maximum of 5 for it to still be a choice on the other side.
I think it's funny that the plane that the main character pyromancer is from can't even print good red spells. Compare the red puzzle to any of the other colors. Seriously, 1 damage? Really? You can spend 5 mana to SHOCK something/someone? What the hell is wrong with just reprinting shock?
I do get that we have two decent to the face burn spells in standard already, but this is like... the pyromancer plane. One would think that the pyromancers would have better spells.
You find it funny but it is one of the biggest flavor wins in quite a while. Chandra was seen as dangerous because the plane has been working to suppress the dangerous side of red while embracing its non destructive parts full force. This is most certainly not "the pyromancer plane" this is as opposite you can be without actually being the opposite(cryomancers). This plane hates Pyromancers our beloved walker was hunted down for this exact reason, if that isn't a compelling story reason to tone down burn significantly I'm not sure what is.
Everyone here is right but I think this needs mentioning. There is a card that does exactly what you want so you can see how its already worded and just add the "may" to it. Gruul Ragebeast. It specifically calls out its name to say it fights to clear up misunderstandings such as yours. If you look through cards that grant abilities or do similar things you can see that other than slivers they always call out themselves when they are meant to grant themselves the ability only to remove confusion.
If you push her to CMC 4 then she can make 1/1 lifelink creatures on her +, but why do they sac to add mana? It doesn't really play into her other abilities or her lore. If you aren't dead set on making tokens with her + I can see an interesting twist on her purification/immunity by using a similar effect to Kiora but on your own creatures. Like "+1: Until your next turn, up to one target creature gains lifeline, prevent all damage that would be dealt to that creature." This effect can probably be done with her still at 3 CMC. If it is too aggressive you can even give the creature Defender which makes it very interesting to use on other players creatures. A lot of these decisions are based on how pushed you want her to be, should she just barely be playable or do you want a Mindsculpter?
For the wording replace becomes with is so you get (S can be paid with one mana of any color. This spell is the color or colors of the mana used to pay S in addition to its other colors.)
That way its clear that there is no point where you can act before the spell's colors are assigned.
Though you still run into a problem with some spells like your Shimmering Strike. With the way it works you can't actually target anything but black creatures regardless of what mana you spend on S. Because you choose targets long before you pay cost. There is an easy fix that just makes it weird to read, we use Pyroblast. So Shimmering Strike become Destroy target creature if it shares a color with Shimmering Strike
Also for Gleaming Plate you need to add the extra phrase, This doesn't remove Gleaming Plate. Otherwise it would fall off immediately after equipping.
For color caring mechanics. Because you already have black hating on what isn't it you can go the same with red but hate on Basic land types.
You have to reveal the libraries to make them non hidden information, otherwise your opponent can 'fail to find' which goes against the spirit of the card, unless you wanted that as an option. I'm fairly certain I've got the wording right here but it could probably be done better.
Also did you mean Unrequited Feelings?
The current ability has the exile and choice of land as separate abilities so you exile first, these cards don't go into any particular pile as would happen with something like Ashiok, Nightmare Weaver. Then you look at any and all face up lands cards in exile and choose one of them regardless of who owns it or how it got into exile, Crumble to Dust, Delve for Dig Through Time, her own ability, and you can play that land. So long story short, yes you can hit previously exiled lands with her ability.
For reference, template for multiple abilities on an emblem Sarkhan, the Dragonspeaker. For an emblem granting abilities Koth of the Hammer.
Her firsts ability I assume wants to be able to pick a card just exiled so it can't target.
For reference Chandra, Pyromaster
To demonstrate on with your Gleaming Plate as a reference
Addmitedly with this design there is little need for the actual S as it can easily be replaced with generic mana and simply spell out what needs to be done. Though if it ends up significant giving it its own symbol is a good way of showing that it is a mechanic
#2 has the exact same problem as the original only with a significant deck building restraint. "only run Blightsteel Colossus." Although now there is no longer that realistic option of your opponent being able to stop you with a random Fiend Hunter or Leonin Relic-Warder.
#3 Is by far the best for the intended effect of mimicking Guild Feud. It still combos into Blightsteel, but considering the other 1 was a one card combo turning this into a two card combo with Worldly Tutor is much better.
(S can be paid with one mana of any color. This spell is the color or colors of the mana used to pay S in addition to its other colors.)
That way its clear that there is no point where you can act before the spell's colors are assigned.
Though you still run into a problem with some spells like your Shimmering Strike. With the way it works you can't actually target anything but black creatures regardless of what mana you spend on S. Because you choose targets long before you pay cost. There is an easy fix that just makes it weird to read, we use Pyroblast. So Shimmering Strike become Destroy target creature if it shares a color with Shimmering Strike
Also for Gleaming Plate you need to add the extra phrase, This doesn't remove Gleaming Plate. Otherwise it would fall off immediately after equipping.
For color caring mechanics. Because you already have black hating on what isn't it you can go the same with red but hate on Basic land types.