Few cards create them, and few of those cards see regular play
(9/19/2025) If an effect allows you to play a land or cast a spell from among a group of cards, you may play or cast a modal double-faced card with any face that fits the criteria of that effect
Your opponent will be stuck playing one new mana per turn
Whenever a creature you control dies, put a loyalty counter on Lolth, Spider Queen.0: You draw a card and you lose 1 life.3: Create two 2/1 black Spider creature tokens with menace and reach.8: You get an emblem with Whenever an opponent is dealt combat damage by one or more creatures you control, if that player lost less than 8 life this turn, they lose life equal to the difference
You could do it on turn 2 and sacrifice a mana land for a key card you discarded with your two cost like a sorcery that discards and then draws, such as Cathartic Reunion
Rare cards often fetch higher prices due to their limited availability