Cueva is a place of weird mutated wilds. The few sentient beings that live (all of which are humans) are fighting a losing battle and they'll soon be overwhelmed

Five new mechanics appear in Cueva

Unity is a pseudo keyword that says 'if you control four or more creatures, do X'. This represents the humans using their superior numbers to defeat the forces of the wild. This keyword is in white

Fluctuate is a keyword that says (MANA: Switch the power and toughness of this creature until end of turn). This represents the creatures that live on the island of Miriamba, long ago the site of ancient and powerful magic which mutates everything around it. This keyword is in blue

Pollute N is a keyword that says (creatures blocking or blocked by this creature get -N/-N). This represents the disgusting mutated and disease carrying creatures that live in the Carbosa Swamp. This keyword is in black

Bloodthirst is returning from Ravnica block and M12. It represents those creatures that smell blood and pounce. In this set, this ability is exclusively in red

Primal N is a keyword that says 'you may have this creature enter the battlefield with no abilities and N +1/+1 counters on it '. This represents the very biggest creatures, the apex predators who would eat all in their path. This is green

While these abilities don't have much to do with each other, they all involve creatures. That's because the theme of this set is creatures matter. There are more creatures than usual and creature combat is even more important than usual SO HA CONTROL PLAYERS (WAIT I PLAY CONTROL DO I HATE MYSELF???)

Here's a nice teaser

Alanza, Leader of Humans
Legendary Creature- Human Soldier (M)
Unity- If you control four or more creatures, creatures you control get +2/+2
2/3

Wait creatures already matter how can I make a creatures matter set? BECAUSE I SAID SO (a fantastic approach to set design)

Also teleport can be done for nonmana costs but I can't be bothered to edit the OP

Teleport and pollute seem like they would seriously warp the environment in any quantity significant enough to be keyworded. The other three keywords are neat though. I like how heavily this set encourages attacking with creature swarms.

Pollute is ridiculous and is now Pollute N (Creatures blocking or blocked by this creature get -N/-N)

Teleport is ridiculous and is being changed to... something.

In the meantime

Ellia's Experimentation
Instant (U)
Put five -1/-1 counters on target creature. Draw a card

How about

Fluctuate (MANA: Switch the power and toughness of this creature until end of turn)

Also... DUEL LAND CYCLE!!!!!!!!!!

Ice Expanses
Land (R)
~ enters the battlefield tapped unless you reveal a white or blue creature card from your hand
: Add or to your mana pool
(ART: endless ice with only an abandoned, rotting, but tall tower in sight)

Flooded Cemetery
Land (R)
~ enters the battlefield tapped unless you reveal a blue or black creature card from your hand
: Add or to your mana pool
(Art: A huge cemetery with water nearly at the top of the gravestones)

Alpine Battleground
Land (R)
~ enters the battlefield tapped unless you reveal a red or black creature card from your hand
: Add or to your mana pool
(ART: A mountain with dead souls floating around it)

Burnt Jungle
Land (R)
~ enters the battlefield tapped unless you reveal a red or green creature card from your hand
: Add or to your mana pool
(Art: A couple of trees but with many many blackened stumps)

Wolf-Claimed City
Land (R)
~ enters the battlefield tapped unless you reveal a green or white creature card from your hand
: Add or to your mana pool
(Art: Grand buildings, but all are abandoned. Wolves prowling around)

Unreachable Peak
Land (R)
~ enters the battlefield tapped unless you reveal a red or white creature card from your hand
: Add or
(Art: Humans and small tents on the top of a mountain. Mutated beasts are standing below, eating human corpses. The shell of a house is visible below)

Temple to Old Gods
Land (R)
~ enters the battlefield tapped unless you reveal a white or black creature card from your hand
: Add or to your mana pool
(Art: A temple on a grand scale. Humans huddle inside. Horrors outside claw at the windows.)

Mass Graves
Land (R)
~ enters the battlefield tapped unless you reveal a black or green creature card from your hand
: Add or to your mana pool
(Art: A bedraggled corpse is in a pit alongside a lot of skeletons. Huge ants have already started to eat her flesh)

Trashed University
Land (R)
~ enters the battlefield tapped unless you reveal a blue or red creature card from your hand
: Add or to your mana pool
(Art: Empty bookshelves. Birds are eating some sort of magical energy)

Sunken Forest
Land (R)
~ enters the battlefield tapped unless you reveal a blue or green creature card from your hand
: Add or to your mana pool.
(Art: A forest in which only the very tops of the trees are above water. A human family is hanging onto a tree and screaming)

Mood for all: Ha the humans in Innistrad thought they had it bad

Note: I decided to print all of them in one set because I think standard should have all of them at once to make different decks viable. Also the block (lol that will get completed) will only be two sets

Ellia, the Endbringer
Planeswalker-Ellia (M)
+1 Put a -1/-1 counter on target creature
-3 Draw a card for each creature that died this turn
-9Each creature you don't control gets -10/-10 until end of turn
4

Major character bro. Ellia is from the MEM. Read their stuff. This whole mess on this plane is her fault by the way

Beryl, the Heart Scarred
Planeswalker-Beryl (M)
+1 You gain 2 life
-2 Beryl, the Heart Scarred deals 2 damage to target player
-8 Beryl deals 10 damage to each creature and each player
3

Beryl is a minor character but also from the MEM. She basically turns up accidentally and tries to help but she is USELESS!

Imarivo Otiera
Planeswalker-Ilarico
+1 Create a 2/2 green beast token
-2 Reveal the top five cards of your library. Put a creature card from among them into your hand and the rest into your graveyard
-11 Search your library for any number of creature cards and put them onto the battlefield tapped
3
Ilarico is not from the MEM. He believes that the humans deserve to be overrun by nature. He is a native to Cueva.

And a reprint with new flavour

Life's Legacy
Sorcery (R)
As an additional cost to cast ~, sacrifice a creature
Draw cards equal to the sacrificed creatures power
"Your innards are very interesting"- Ellia

And a nice ACTUAL COMMON

Corrupting Mutation
Creature-Beast Horror (C)
Pollute 1(Creatures blocking or blocked by this creature get -1/-1)
1/1

Poor, poor Beryl. Even her card sucks.

Also Illarion needs like, a cost

I meant Ilarico but that did make me realise that his name is too close to Illarion. Hmmm

Also Corrupting Mutation needs flavour. But in the mean time, here's some actual flavour (and a reflavoured reprint)

Vow of the Knowledge Seekers
I commit to the finding and archiving of knowledge for the rest of my days. I will not cower and hide like the rest of my kind. I will go out bravely, increasing what we know so we may take back our world, not by throwing ourselves hopelessly, but by cunning.
–--------------------------------------------------

Erus Libra Bestiarus
Introduction
Once, the humans were strong. We ruled. The world were shaped to our needs and wants, and our temples and monuments stretched up into the sky. Now, we are reduced to a few small settlements, with some still fighting a losing battle to regain our dominance. This is due to the mutation of the beasts. The beasts listed below are the types that are most common

Bestus Lithum (stonebeasts, betias pedra)
The stonebeast are quite rare. These animals have skin of different stones and metals most commonly granite. They seem to be very pack-motivated animals and each pack, we speculate, has a leader made out of iron, which they value highly. These are very hard to kill because of the material of the skin. Either large force or death magic is required

Bestus Alterto (mutators, camba mutacion)
The home of these beasts is the Miriamba Islands, but sometimes they move out towards the Mirika plains to hunt humans. We speculate the spell that caused this mass mutation is there, so these beasts are among the strangest. We managed to catch and vivisect one, and we see many characteristics of birds inside them, but these are land creatures and have no wings. The common name of mutators is misleading, as all the animals in this land are mutated. But the reason it has this name (and the scientific name Bestus Alterto meaning beast of change), is because its skin stretches and changes into different shapes and consistencies. This even happens after death, so we needed a freezing spell for the vivisection

Bestus Inquinium (corruptions, impurnago)
These beats pollute and corrupt the land around them. Where they walk, trees shrivel and people get sick. These beasts spread disease and decay, and these are probably the worst scourge of human settlements, because the people who survive die of illness. We can't study these creatures unless we wish to die, but we think they breed in the Carbosa swamp. We can't go there though, because it would kill us. All we know is from scrying spells.

Bestus Sanguine (Bloodbeasts, Sangra betasa)
These beats seem not to live on flesh but blood. They can smell blood from a huge distance away, and whenever one bleeds, a huge pack comes and attacks the area. Most human settlements drive people away to die as soon as they bleed, even children, but we find this inhumane. Luckily, we have underground vaults in which to store books, and which the Bloodbeasts can't get to. We aren't sure what animals these evolved from, but we think that they might have originally been something called a 'mouse'.

Bestus Gigantio (Crushers, Titarando)
These, we know the most about. Calling them one species is misleading, as they are evolved from different species, but we have grouped them for convenience. You may find more detail, of course, later in this volume. The thing is, these are just different huge creatures. There are birds, too huge to fly and this now flightless. There are wolves with feet as big as houses. There are boars. There are even men, their twisted form called giants (note: some people dispute the status of giants as mutations and think they are just natural beings).

Wolf Crusher
Creature- Giant Wolf (C)
Trample
Predator- At the beginning of your upkeep, sacrifice ~ unless it has the greatest power among creatures
5/5

That seems more like an uncommon to me.

Yes that also seems more like an uncommon to me (he says, conveniently agreeing with the experienced person)

Crusher of Settlements
Creature- Giant Beast (C)
Predator- At the beginning of your upkeep, if ~ has the highest amount of power among all creatures, draw a card
4/3

That, too, also seems more like an uncommon to me. Maybe make it an ETB trigger?

Wait the green mechanic is ****. It is not only win-more but rewards a lot the player going first

Heft- When ~ enters the battlefield, you may put a +1/+1 counter on it. If you do not, put a change counter on it and it gains STUFF!!!!

Is that ok? Any name suggestions?

Something like this, maybe:

Bear Scorpion

Creature - Bear Scorpion (C)
1/1

Adapt (You may have this creature enter the battlefield with a +1/+1 counter on it.)
As long as Bear Scorpion has no +1/+1 counters on it, it has deathtouch.

Good.

I STEAL YOUR MECHANIC AND YOUR CARD!

(No seriously that's a really good card I'm stealing it)

Except the name needs work

Um...

Clawed Bear (Whatever, that'll do)