Coat of Arms

Mana cost: {5}
Type: Artifact
Set: The Lost Caverns of Ixalan Commander #108 (rare)
Price: $23.73 USD

Each creature gets +1/+1 for each other creature on the battlefield that shares at least one creature type with it. (For example, if two Goblin Warriors and a Goblin Shaman are on the battlefield, each gets +2/+2.)

Coat of Arms has 20 printings, first in Exodus (1998). EDHREC ranks it #966 among Commander cards. It appears most in Krenko, Mob Boss decks (12,029 on EDHREC). 1 public deck on TCG runs it. It has 3 official rulings.

Legality

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

Public decks that run Coat of Arms

Everyone's Invited - Secret Lair Drop - WUBRG EDH Precon Decklist, led by Morophon, the Boundless

Commanders that run Coat of Arms most

Deck counts from EDHREC.

Krenko, Mob Boss: 12,029 decks
Lathril, Blade of the Elves: 6,256 decks
Edgar Markov: 5,435 decks
Marrow-Gnawer: 4,992 decks
The First Sliver: 3,803 decks
Shroofus Sproutsire: 3,213 decks
Chatterfang, Squirrel General: 2,939 decks
Rin and Seri, Inseparable: 2,855 decks

Often played with Coat of Arms

Cards that show up in the same decks on EDHREC.

Rulings

2004-10-04: If you have a creature with more than one creature type, count all creatures which have either creature type.
2004-10-04: If a creature has more than one creature type, and one of those types matches the creature you are calculating for, then count that creature. Only one type needs to match in order to get counted.
2009-10-01: Sharing multiple creature types doesn't give an additional bonus. Coat of Arms counts creatures, not creature types.