Primal Vigor | Magic: The Gathering
Formats Primal Vigor is Legal in
Official Oracle Text for Primal Vigor
If one or more +1/+1 counters would be placed on a creature, twice that many +1/+1 counters are placed on that creature instead.
Official Rulings for Primal Vigor
10/17/2013 : Primal Vigor affects permanents that “enter the battlefield with” a certain number of counters. For example, if a creature would normally enter the battlefield with three +1/+1 counters on it, it will enter with six +1/+1 counters on it.
10/17/2013 : If there are two Primal Vigors on the battlefield, the number of tokens or +1/+1 counters is four times the original number. If there are three on the battlefield, the number of tokens or +1/+1 counters is eight times the original number, and so on.