Cheapest priced copy (Ice Age): $3.49 at Card Kingdom, near mint, their price list as of .
Mudslide 
Enchantment · Rare · Ice Age · #204
Creatures without flying don't untap during their controllers' untap steps.
At the beginning of each player's upkeep, that player may choose any number of tapped creatures without flying they control and pay {2} for each creature chosen this way. If the player does, untap those creatures.
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper
1 printing · $3.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Ice Age | 204 | Rare | $3.49 | — |
One ruling from Wizards of the Coast
- 1 October 2008First the player chooses all the tapped creatures they would like to untap this way. Then the entire payment is made at once, then all of those creatures untap at the same time. If the entire payment can’t be paid (because the player chose too many creatures, for example), none of it is paid and none of those creatures untap.