Is Strength of the Tajuru legal in Standard, Modern, and Commander?

Strength of the Tajuru is legal in: Modern, Legacy, Vintage, Commander.

Strength of the Tajuru

Q: What type of card is Strength of the Tajuru?

Strength of the Tajuru is an Instant. Its oracle text reads: "Multikicker {1} (You may pay an additional {1} any number of times as you cast this spell.) Choose target creature, then choose another target creature for each time this spell was kicked. Put X +1/+1 counters on each of them."