Blast Zone
Land
This land enters with a charge counter on it.
: Add 
.
, : Put X charge counters on this land.
, , Sacrifice this land: Destroy each nonland permanent with mana value equal to the number of charge counters on this land.
Illustrated by
Edge of Eternities: Stellar Sights#92RareEnglishLegality
Rulings
May 3, 2019
An activation cost of means that you pay twice X. If you want X to be 3, you pay 
to activate Blast Zone’s ability.
May 3, 2019
Tokens that aren’t a copy of something else don’t have a mana cost. Anything without a mana cost normally has a converted mana cost of 0.
May 3, 2019
If a permanent has in its mana cost, X is considered to be 0.