Cheapest priced copy (Guilds of Ravnica): $1.49 at Card Kingdom, near mint, their price list as of .
Mausoleum Secrets 
Instant · Rare · Guilds of Ravnica Promos · #75p
Undergrowth — Search your library for a black card with mana value less than or equal to the number of creature cards in your graveyard, reveal it, put it into your hand, then shuffle.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
3 printings · $1.49 to $14.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Guilds of Ravnica | 75 | Rare | $1.49 | $4.49 |
| Guilds of Ravnica Promos | 75p | Rare | $2.79 | $14.99 |
| Guilds of Ravnica Promos | 75s | Rare | — | $5.49 |
4 rulings from Wizards of the Coast
- 5 October 2018Creature cards with other types, such as artifact creature cards, count for undergrowth abilities.
- 5 October 2018If a card in your library has {X} in its mana cost, X is considered to be 0.
- 5 October 2018Because tokens aren’t cards, they never count for undergrowth abilities.
- 5 October 2018A land card that produces black mana, even a Swamp, normally has no color.