Boundary of Worlds
Land
As Boundary of Worlds enters the battlefield, choose Kami or Mortal. An opponent creates a land with the other ability.

• Kami — : Add one mana of any color. Spend this mana only to cast Spirit or Arcane spells.
• Mortal — : Add one mana of any color. Spend this mana only to cast non-Spirit, non-Arcane spells.

Next is Ravnica

The Fine Print
Enchantment
At the beginning of each end step, if each player cast one or less spell this turn, then each player draws a card.
Contrary to common misconception, the Azorius do allow some finagling with their legislature ... at least until it stops working as they intended.

Atmophora
Creature — Jellyfish
Atmophora enters the battlefield with a flying counter.
Splice onto creature
"The Guardian Project proved necessary. Let us accelerate." — Prime Speaker Vannifar
2/2

Wrong Street

Instant (C)
Destroy target creature.
Deceive (You may cast this for its Deceive cost by returning an attacking unblocked creature you control to its owner's hand.)
In Ravnica's sprawling backstreets, it's easy to get lost and even easier to be found.

Rack the Brain
Instant
Replicate — Discard a card at random
As an additional cost to cast this spell, discard a card.
Draw two cards.
Jump-start
"A nice sparkshower always gets me thinking." — Mizzix of the Izmagnus

Burning Tree Reveler
Creature - Human Shaman
Riot
: Add . Activate this ability only if ~ entered the battlefield this turn or if ~ has a +1/+1 counter on it.
[1/1]

Tithespell
Instant
Counter target spell unless its controller pays 4 life. If they do, you gain 4 life and create two Treasure tokens.
"All sins are forgivable. All graces are refundable."

Initiate's Signet

Artifact (U)
Initiate's Signet enters the battlefield tapped.
When Initiate's Signet enters the battlefield, choose two different colors.
: Add one mana of either of the chosen colors.

Communal Gate
Land - Gate
~ enters the battlefield tapped.
: Add .
: Add one mana of any color another Gate you control could produce.

Dominaria

The Folly of Kirtar
Enchantment — Saga
I, II - Exile target creature until The Folly of Kirtar leaves the battlefield.
III - Destroy all creatures.

Laquatus's Archivist
Creature - Merfolk Wizard
: Draw a card and reveal it. If it isn't a historic card, discard it.
"History cares little for those without a name or value."
[1/3]

I was creating a card to represent Chainer turning into snakes and I realized I just recreated Nefarious Lich.

Gibbering Remnants
Creature — Nightmare Horror
When Gibbering Remnants enters the battlefield, target opponent exiles X cards from their hand until leaves the battlefield.
Gibbering Remnants gets +1/+1 for each card exiled with it.
Put a card exiled with Gibbering Remnants into its owner's hand: Gibbering Remnants gains indestructible until end of turn. Tap it.
0/0

Liberate the Arena
Sorcery
Untap and gain control of target creature you don't control until end of turn. It gains +1/+0, haste, and hexproof from its owner until end of turn

Chainer's Passage
Sorcery
Draw five cards and reveal them. Discard all nonland cards drawn this way.
To become a full dementist, Chainer journeyed into Krosa to draw inspiration from the feral beauty to craft new nightmares.

For Odyssey block.

Skellum, Mad Mentor
Legendary Creature — Human Minion
Whenever you discard one or more cards for the first time each turn, a random nonland card in your hand perpetually gains madness. The madness cost is equal to its mana cost.
When Skellum dies, return target card with madness from your graveyard to your hand.
3/1

redacred

We're on Dominaria. The Gruul are from Ravnica.

I am completely mind blank right now

Carthalion Lotus
Legendary Artifact
, Discard a card named Carthalion Lotus: Add three mana of any one color.
"All other pale in comparison to the original," - Mistress of House Scarlet.

Temporal Maze
Land
: Add .
, : Target attacking creature phases out.