Door of Destinies

Mana cost: {4}
Type: Artifact
Set: Tales of Middle-earth Commander #277 (rare)
Price: $4.52 USD

As this artifact enters, choose a creature type.
Whenever you cast a spell of the chosen type, put a charge counter on this artifact.
Creatures you control of the chosen type get +1/+1 for each charge counter on this artifact.

Door of Destinies has 13 printings, first in Morningtide (2008). EDHREC ranks it #1,087 among Commander cards. It appears most in Éowyn, Shieldmaiden decks (9,615 on EDHREC). 4 public decks on TCG run it. It has 2 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 Door of Destinies

Avengers Assemble - Marvel Super Heroes, led by Captain America, Team Leader
Riders of Rohan - Tales of Middle-earth Commander, led by Éowyn, Shieldmaiden
Vampiric Bloodlust - Commander 2017, led by Edgar Markov
We Are The Borg - Star Trek Commander, led by The Borg Queen

Commanders that run Door of Destinies most

Deck counts from EDHREC.

Éowyn, Shieldmaiden: 9,615 decks
Edgar Markov: 8,929 decks
Captain America, Team Leader: 4,002 decks
The First Sliver: 3,675 decks
Marrow-Gnawer: 3,595 decks
Krenko, Mob Boss: 2,922 decks
Lathril, Blade of the Elves: 2,415 decks
Morophon, the Boundless: 2,358 decks

Often played with Door of Destinies

Cards that show up in the same decks on EDHREC.

Rulings

2008-04-01: If you cast a creature spell of the chosen type, Door of Destinies will get a charge counter before the creature enters. The creature will enter with the additional boost to its power and toughness.
2013-07-01: Creature types, such as Human or Sliver, appear after the dash on the type line of creatures. Notably, artifact is not a creature type. A creature may have more than one creature type, such as Goblin Warrior. Such a creature would benefit from Door of Destinies if the chosen creature type was Goblin or Warrior.