Eren and Eren, 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.