Mox Ruby is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

: Add .

How it works : Mox Ruby

Original English text — Wizards of the Coast / Scryfall

No additional ruling has been published for this card.

Popular combos

Real combos played by the community, sorted by popularity.

#1
Cavalier of Dawn + Infinite Reflection + March of the Machines + Mox Ruby
Infinite creature tokensInfinite death triggersInfinite creature ETBInfinite creature LTB
1Cast Mox Ruby by paying .
2Mox Ruby enters the battlefield as a copy of Cavalier of Dawn.
3Copy of Cavalier of Dawn enter-the-battlefield ability triggers, destroying itself and creating you a 3/3 Golem token.
4Copy of Cavalier of Dawn dies, triggering itself, returning Mox Ruby from your graveyard to your hand.
5Repeat.

#1
Cavalier of Dawn + Infinite Reflection + March of the Machines + Mox Ruby
Infinite creature tokensInfinite death triggersInfinite creature ETBInfinite creature LTB
1Cast Mox Ruby by paying .
2Mox Ruby enters the battlefield as a copy of Cavalier of Dawn.
3Copy of Cavalier of Dawn enter-the-battlefield ability triggers, destroying itself and creating you a 3/3 Golem token.
4Copy of Cavalier of Dawn dies, triggering itself, returning Mox Ruby from your graveyard to your hand.
5Repeat.

Interactions with other cards

These cards' text mentions Mox Ruby.

Ruby Collector

When you attack with three or more creatures, conjure a card named Mox Ruby into your hand. This ability triggers only once. {1}{R}: Creatures you control get +1/+0 until end of turn.