MTG Buy-A-Box Promos Rin and Seri, Inseparable

Whenever you cast a Dog spell, create a 1/1 green Cat creature token. Whenever you cast a Cat spell, create a 1/1 white Dog creature token. {R}{G}{W}, {T}: Rin and Seri deals damage to any target equal to the number of Dogs you control. You gain life equal to the number of Cats you control.