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, Inseparable deals
damage to any target equal to the number of
Dogs you control. You gain life equal to the
number of Cats you control.