Desperate Ritual

Add {R}{R}{R}.
Splice onto Arcane {1}{R} (As you cast an Arcane spell, you may reveal this card from your hand and pay its splice cost. If you do, add this card's effects to that spell.)

Demand Answers

As an additional cost to cast this spell, sacrifice an artifact or discard a card.
Draw two cards.

Big Score

As an additional cost to cast this spell, discard a card.
Draw two cards and create two Treasure tokens. (They're artifacts with "{T}, Sacrifice this token: Add one mana of any color.")

Mountain

Mogis, God of Slaughter

Indestructible
As long as your devotion to black and red is less than seven, Mogis isn't a creature.
At the beginning of each opponent's upkeep, Mogis deals 2 damage to that player unless they sacrifice a creature of their choice.

Swamp

Dark Ritual

Sol Ring

Thrill of Possibility

As an additional cost to cast this spell, discard a card.
Draw two cards.

Talisman of Indulgence

{T}: Add {C}.
{T}: Add {B} or {R}. This artifact deals 1 damage to you.

Citadel of Pain

At the beginning of each player's end step, this enchantment deals X damage to that player, where X is the number of untapped lands they control.

Spreading Plague

Whenever a creature enters, destroy all other creatures that share a color with it. They can't be regenerated.

Arcane Signet

{T}: Add one mana of any color in your commander's color identity.

Animate Dead

Enchant creature card in a graveyard
When this Aura enters, if it's on the battlefield, it loses "enchant creature card in a graveyard" and gains "enchant creature put onto the battlefield with this Aura." Return enchanted creature card to the battlefield under your control and attach this Aura to it. When this Aura leaves the battlefield, that creature's controller sacrifices it.
Enchanted creature gets -1/-0.

Cabal Ritual

Add {B}{B}{B}.
Threshold — Add {B}{B}{B}{B}{B} instead if there are seven or more cards in your graveyard.

Pyretic Ritual

Abrade

Choose one —
• Abrade deals 3 damage to target creature.
• Destroy target artifact.

Manabarbs

Whenever a player taps a land for mana, this enchantment deals 1 damage to that player.