Cheapest priced copy (Fallout): $11.99 at Card Kingdom, near mint, their price list as of .
Rampaging Yao Guai 
Creature — Bear Mutant · 2/2 · Rare · Fallout · #401
Vigilance, trample
This creature enters with X +1/+1 counters on it.
When this creature enters, destroy any number of target artifacts and/or enchantments with total mana value X or less.
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper
4 printings · $11.99 to $22.99 at Card Kingdom
2 rulings from Wizards of the Coast
- 8 March 2024If a permanent has {X} in its mana cost, X is 0 when determining its mana value.
- 8 March 2024A token that's not a copy of something else normally won't have a mana cost. Anything without a mana cost normally has a mana value of 0.