Combustible Gearhulk

First strike
When Combustible Gearhulk enters, target opponent may have you draw three cards. If the player doesn't, you mill three cards, then Combustible Gearhulk deals damage to that player equal to the total mana value of those cards.

Rhystic Cave

{T}: Choose a color. Add one mana of that color unless any player pays {1}. Activate only as an instant.

Sin Prodder

Menace
At the beginning of your upkeep, reveal the top card of your library. Any opponent may have you put that card into your graveyard. If a player does, Sin Prodder deals damage to that player equal to that card's mana value. Otherwise, put that card into your hand.

Graven Cairns

{T}: Add {C}.
{B/R}, {T}: Add {B}{B}, {B}{R}, or {R}{R}.

Breaking Point

Any player may have Breaking Point deal 6 damage to them. If no one does, destroy all creatures. Creatures destroyed this way can't be regenerated.

Wall of Vipers

Defender (This creature can't attack.)
{3}: Destroy Wall of Vipers and target creature it's blocking. Any player may activate this ability.

Longhorn Firebeast

When Longhorn Firebeast enters, any opponent may have it deal 5 damage to them. If a player does, sacrifice Longhorn Firebeast.

Oona's Prowler

Flying
Discard a card: Oona's Prowler gets -2/-0 until end of turn. Any player may activate this ability.

Dragonskull Summit

Dragonskull Summit enters tapped unless you control a Swamp or a Mountain.
{T}: Add {B} or {R}.

Browbeat

Any player may have Browbeat deal 5 damage to them. If no one does, target player draws three cards.

Book Burning

Any player may have Book Burning deal 6 damage to them. If no one does, target player mills six cards.

Dash Hopes

When you cast this spell, any player may pay 5 life. If a player does, counter Dash Hopes.
Counter target spell.

Well of Knowledge

{2}: Draw a card. Any player may activate this ability but only during their draw step.

Vexing Devil

When Vexing Devil enters, any opponent may have it deal 4 damage to them. If a player does, sacrifice Vexing Devil.

Mountain

Blood Crypt

({T}: Add {B} or {R}.)
As Blood Crypt enters, you may pay 2 life. If you don't, it enters tapped.