Cheapest priced copy (Dominaria United): $0.35 at Card Kingdom, near mint, their price list as of .
Writhing Necromass 
Creature — Zombie Giant · 5/5 · Common · Dominaria United · #115
This spell costs {1} less to cast for each creature card in your graveyard.
Deathtouch
Legal inCommanderPioneerModernLegacyVintagePauper
Not legal inBrawlStandard
1 printing · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Dominaria United | 115 | Common | $0.35 | $0.49 |
2 rulings from Wizards of the Coast
- 9 September 2022To determine the total cost of a spell, start with the mana cost or alternative cost you’re paying, add any cost increases, then apply any cost reductions (such as that of Writhing Necromass). The mana value of the spell is determined by only its mana cost, no matter what the total cost to cast that spell was.
- 9 September 2022Writhing Necromass’s first ability can’t reduce the {B} in its cost.