Cheapest priced copy (Commander 2017): $0.49 at Card Kingdom, near mint, their price list as of .
Mercurial Chemister 
Creature — Human Wizard · 2/3 · Rare · Return to Ravnica · #180
{U}, {T}: Draw two cards.
{R}, {T}, Discard a card: This creature deals damage to target creature equal to the discarded card's mana value.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
4 printings · $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Commander 2017 | 180 | Rare | $0.49 | — |
| Commander 2020 | 221 | Rare | $0.49 | — |
| The List | RTR-180 | Rare | $0.49 | — |
| Return to Ravnica | 180 | Rare | $0.49 | $0.49 |
2 rulings from Wizards of the Coast
- 1 October 2012If the discarded card has no mana symbols in its upper right corner (because it's a land card, for example), its mana value is 0.
- 1 October 2012If the discarded card has {X} in its mana cost, X is 0.