Cheapest priced copy (Coldsnap): $0.35 at Card Kingdom, near mint, their price list as of .
Magmatic Core 
Enchantment · Uncommon · Coldsnap · #91
Cumulative upkeep {1} (At the beginning of your upkeep, put an age counter on this permanent, then sacrifice it unless you pay its upkeep cost for each age counter on it.)
At the beginning of your end step, this enchantment deals X damage divided as you choose among any number of target creatures, where X is the number of age counters on it.
Legal inCommanderModernLegacyVintage
Not legal inBrawlStandardPioneerPauper
1 printing · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Coldsnap | 91 | Uncommon | $0.35 | $0.49 |
4 rulings from Wizards of the Coast
- 15 July 2006Each target must be assigned at least 1 damage.
- 15 July 2006The damage is divided when Magmatic Core’s ability triggers. Increasing or decreasing the number of age counters on Magmatic Core after the ability triggers but before it resolves has no effect on the amount of damage that’s dealt.
- 15 July 2006If Magmatic Core has no age counters on it, the only number of targets the ability can have is zero.
- 12 July 2019You can choose zero targets. In this case, Magmatic Core deals no damage.