If one or more tokens would be created, twice that many of those tokens are created instead.
If one or more +1/+1 counters would be put on a creature, twice that many +1/+1 counters are put on that creature instead.
10/17/2013 It doesn’t matter who controls the tokens or the creature that the +1/+1 counters are being placed on.
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.