Kederekt, Gloomy Necropolis
Land (R)
Kederekt enters the battlefield tapped unless it was unearthed.
, , Sacrifice Kederekt: Add .
Unearth — sacrifice a creature (Sacrifice a creature: Return this card from your graveyard to the battlefield. Exile it at the beginning of the next end step or if it would leave the battlefield. Unearth only as a sorcery.)

Zendikar

Cache-Line Runner
Creature — Kor Scout
Landfall — Whenever a land enters the battlefield under your control, if you control fewer lands than each other opponent, create two Treasures.
"The less we have, the more that little is worth."
1/3

Muckwing Demon
Creature - Elemental Demon (R)
Flying
At the beginning of your upkeep, sacrifice a non-Swamp land. If you do, create two Swamp tokens.
It rose to reclaim the wastes, but it didn't stop there.
5/4

Pressure
Instant
Untap target land an opponent controls. You gain control of it until your next turn.
The greatest wonders and the most terrible dangers are constantly created by the land's roiling.

Stone Rain + Threaten?

Nissa’s Touch —
Enchantment — Aura (R)
Enchant land
Enchanted land is a 3/3 creature that’s still a land.
Totem armor

Kiora, Cosi Reborn
Legendary Planeswalker — Kiora
Creatures you control with power equal to or greater than Kiora's loyalty have hexproof.
: Until your next turn, target creature you control has ": Counter target spell unless its controller pays , where X is this creature's power."
: Draw a card.
: You get an emblem with "At the beginning of your end step, if you have four or more cards in hand, create an 8/8 blue Octopus creature token."

Surveyor's Plans —
Artifact (R)
If a land entering the battlefield under your control would cause a triggered ability to trigger, that ability triggers an additional time.
, : Scry 2, then reveal the top card of your library. If it's a land card, put it into your hand.

Floating Horizon
Land
Floating Horizon enters the battlefield tapped and with a charge counter.
: Add .
, Remove a charge counter from Floating Horizon: Add one mana of any color.
, : Exile Floating Horizon and return it to the battlefield.

Innistrad!

Cathar Trainee

Creature -- Human Soldier (C)
Whenever Cathar Trainee attacks or blocks, it gets +1/+1 until end of turn if you control another attacking or blocking Human.
"A silver dagger, wooden stake, blessed water... do I really need to carry all this stuff?"
1/1

On Their Tail —
Enchantment (U)
When On Their Tail enters the battlefield, investigate. (Create a Clue artifact token with “, sacrifice this artifact: Draw a card.)
Activated abilities of Clues you control cost less.

Hellpact
Enchantment
If your life total would become 0 or less, instead you sacrifice two creatures and your life total becomes equal to the number of Demons you control.
A drink that cannot slake. A feast that cannot satiate.

Split the Moon
Sorcery (M)
Exile each double-faced Werewolf you control. For each creature card exiled this way, create a token that's a copy of that card, then create a token that's a copy of that card transformed. (Tokens can't transform.)
As Emrakul shattered its prison, the werewolves saw their other halves face-to-face.

I wish I could find a good wording that didn't use the term "double-faced", since there's no precedent for printing that term on cards.

Stitched Amalgam

Creature -- Zombie Horror (R)
As an additional cost to cast Stitched Amalgam, sacrifice a creature, discard a creature card, and exile a creature card from your graveyard.
Hexproof, trample
A masterwork in depravity.
9/9

Purified Form
Creature — Eldrazi
If a creature you control would transform, you may instead exile that creature and put Purified Form onto the battlefield from your hand.
Hexproof from non-colorless
"I was wrong. There is greater perfection."
4/4

Suspicious Hideout
Land (R)
: Add one mana of any colour. Target opponent investigates.

Theros

Kytheon, the Hero God
Legendary Enchantment Creature — God
Indestructible
As long as your devotion to white is less than five, Kytheon loses all other abilities.
You may cast Aura and sorcery spells as though they had flash during combat.
Whenever Kytheon attacks, each other creature you control gains indestructible.
4/4

Fragile Naiad —
Enchantment Creature — Spirit (R)
Flying
Bestow (If you cast this card for its bestow cost, it’s an Aura spell with enchant creature. It becomes a creature again if it’s not attached to a creature.)
Enchanted creature has “When this creature becomes the target of a spell, sacrifice it.”
When Fragile Naiad becomes the target of a spell, sacrifice it.
2/1