Mount Doom is a legendary land card that acts as a mana fixer for black-red decks, while also bringing two remarkable new effects to the table
Feed the Swarm is a recent addition, signaling that black is getting some access to enchantment removal, albeit a small amount
It's worth noting that while they're bundled together, you can put any Doctor in your command zone with any companion, allowing for all kinds of unique combinations and strategies
you can't really play them in most decks due to colors.) Elemental Bond will generate a tremendous amount of card advantage, and is only green, so it can be played in more decks
While that means you can store +1/+1 counters on a land after a board wipe, its secondary ability also allows you to move things like loyalty counters between planeswalkers
Pioneered the "Free Spell" Design Space Force of Will pioneered free spells with its unique alternate casting cost