Cheapest priced copy (The List): $0.59 at Card Kingdom, near mint, their price list as of .
Planar Collapse 
Enchantment · Rare · The List · #ULG-18
At the beginning of your upkeep, if there are four or more creatures on the battlefield, sacrifice this enchantment and destroy all creatures. They can't be regenerated.
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper
2 printings · $0.59 to $32.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| The List | ULG-18 | Rare | $0.59 | — |
| Urza's Legacy | 18 | Rare | $0.99 | $32.99 |
3 rulings from Wizards of the Coast
- 4 October 2004This ability does not trigger at all if there are not 4 or more creatures on the battlefield. It also checks this at the start of resolution and does nothing if this is not still true.
- 4 October 2004The ability is not optional.
- 15 June 2010If this card is not on the battlefield when the ability resolves, then you can’t sacrifice it. However, you still destroy all creatures.