Cheapest priced copy (Neon Dynasty Commander): $0.49 at Card Kingdom, near mint, their price list as of .
Elemental Mastery 
Enchantment — Aura · Rare · Shadowmoor · #90
Enchant creature
Enchanted creature has "{T}: Create X 1/1 red Elemental creature tokens with haste, where X is this creature's power. Exile them at the beginning of the next end step."
Legal inCommanderModernLegacyVintage
Not legal inBrawlStandardPioneerPauper
2 printings · $0.49 to $12.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Neon Dynasty Commander | 105 | Rare | $0.49 | — |
| Shadowmoor | 90 | Rare | $1.79 | $12.99 |
3 rulings from Wizards of the Coast
- 1 May 2008If the ability is activated after the current turn's End step has begun, the tokens won't be exiled until the next turn's End step.
- 1 May 2008The enchanted creature's power is checked at the time the ability resolves. If the enchanted creature has left the battlefield by then, its last known information is used.
- 1 May 2008The tokens will be exiled in the End step even if Elemental Mastery or the enchanted creature has left the battlefield by then.