Rin and Seri, Inseparable

Mana cost: {1}{R}{G}{W}
Type: Legendary Creature — Dog Cat
Power / toughness: 4 / 4
Set: Core Set 2021 #278 (mythic)
Price: $32.49 USD

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.

Rin and Seri, Inseparable has 6 printings, first in Core Set 2021 (2020). EDHREC ranks it #5,489 among Commander cards. It appears most in Morophon, the Boundless decks (1,194 on EDHREC). 2 public decks on TCG run it. It has 4 official rulings.

Legality

commander: legal
legacy: legal
vintage: legal
pauper: not legal
modern: legal
pioneer: legal
standard: not legal
brawl: legal

Public decks that run Rin and Seri, Inseparable

Everyone's Invited - Secret Lair Drop - WUBRG EDH Precon Decklist, led by Morophon, the Boundless
Raining Cats and Dogs - Secret Lair Drop, led by Rin and Seri, Inseparable

Commanders that run Rin and Seri, Inseparable most

Deck counts from EDHREC.

Morophon, the Boundless: 1,194 decks
Jinnie Fay, Jetmir's Second: 835 decks

Often played with Rin and Seri, Inseparable

Cards that show up in the same decks on EDHREC.

Rulings

2020-06-23: If the chosen target is an illegal target by the time Rin and Seri's last ability tries to resolve, the ability won't resolve. You won't gain life.
2020-06-23: Rin and Seri's first two abilities don't trigger when you cast Rin and Seri.
2020-06-23: An ability that triggers when a player casts a spell resolves before the spell that caused it to trigger. It resolves even if that spell is countered.
2020-06-23: The amount of damage Rin and Seri's last ability deals is determined only as that ability resolves. If Rin and Seri is still on the battlefield, it'll count itself.