Cheapest priced copy (Theros Beyond Death): $0.35 at Card Kingdom, near mint, their price list as of .
Devourer of Memory 
Creature — Nightmare · 2/1 · Uncommon · Theros Beyond Death · #213
Whenever one or more cards are put into your graveyard from your library, this creature gets +1/+1 until end of turn and can't be blocked this turn.
{1}{U}{B}: Mill a card.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
1 printing · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Theros Beyond Death | 213 | Uncommon | $0.35 | $0.49 |
2 rulings from Wizards of the Coast
- 24 January 2020Once Devourer of Memory has been blocked, resolving its triggered ability (perhaps by activating its activated ability) won’t change or undo that block.
- 24 January 2020Devourer of Memory’s triggered ability grants it just +1/+1 each time cards are put into your graveyard from your library, no matter how many cards are put there at once.