Sacred Foundry

({T}: Add {R} or {W}.)
As Sacred Foundry enters the battlefield, you may pay 2 life. If you don't, it enters the battlefield tapped.

Mountain

Battlefield Forge

{T}: Add {C}.
{T}: Add {R} or {W}. Battlefield Forge deals 1 damage to you.

Burning-Tree Emissary

When Burning-Tree Emissary enters the battlefield, add {R}{G}.

Pattern Matcher

When Pattern Matcher enters the battlefield, you may search your library for a card with the same name as another creature you control, reveal it, put it into your hand, then shuffle.

Arid Mesa

{T}, Pay 1 life, Sacrifice Arid Mesa: Search your library for a Mountain or Plains card, put it onto the battlefield, then shuffle.

Skirk Prospector

Mirror March

Whenever a nontoken creature enters the battlefield under your control, flip a coin until you lose a flip. For each flip you won, create a token that's a copy of that creature. Those tokens gain haste. Exile them at the beginning of the next end step.

Krark's Thumb

If you would flip a coin, instead flip two coins and ignore one.

Goblin Dark-Dwellers

Menace
When Goblin Dark-Dwellers enters the battlefield, you may cast target instant or sorcery card with mana value 3 or less from your graveyard without paying its mana cost. If that spell would be put into your graveyard, exile it instead.

Felidar Guardian

When Felidar Guardian enters the battlefield, you may exile another target permanent you control, then return that card to the battlefield under its owner's control.

Kor Skyfisher

Flying
When Kor Skyfisher enters the battlefield, return a permanent you control to its owner's hand.

Plains

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.)

Fiery Gambit

Flip a coin until you lose a flip or choose to stop flipping. If you lose a flip, Fiery Gambit has no effect. If you win one or more flips, Fiery Gambit deals 3 damage to target creature. If you win two or more flips, Fiery Gambit deals 6 damage to each opponent. If you win three or more flips, draw nine cards and untap all lands you control.