Unbound Flourishing

Mana cost: {2}{G}
Type: Enchantment
Set: Secrets of Strixhaven Commander #126 (mythic)
Price: $2.18 USD

Whenever you cast a permanent spell with a mana cost that contains {X}, double the value of X.
Whenever you cast an instant or sorcery spell or activate an ability, if that spell's mana cost or that ability's activation cost contains {X}, copy that spell or ability. You may choose new targets for the copy.

Unbound Flourishing has 4 printings, first in Modern Horizons (2019). EDHREC ranks it #2,594 among Commander cards. It appears most in Zaxara, the Exemplary decks (16,477 on EDHREC). 1 public deck on TCG runs it. It has 14 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 Unbound Flourishing

Quandrix Unlimited - Secrets of Strixhaven, led by Zimone, Infinite Analyst

Commanders that run Unbound Flourishing most

Deck counts from EDHREC.

Often played with Unbound Flourishing

Cards that show up in the same decks on EDHREC.

Rulings

2019-06-14: If the value chosen for X is 0, Unbound Flourishing will double the value to 0 for permanent spells, and copy other spells and abilities.
2019-06-14: The copy has the same value of X.
2019-06-14: If the spell or ability that's copied is modal (that is, it says "Choose one —" or the like), the copy will have the same mode or modes. You can't choose different ones.
2019-06-14: A copy is created even if the spell or ability that caused Unbound Flourishing's ability to trigger has been countered by the time that ability resolves. The copy resolves before the original spell.
2019-06-14: Spells with additional costs that include {X} won't be affected by Unbound Flourishing. {X} must be in the spell's mana cost.
2019-06-14: If a permanent has an ability that triggers when it's cast and that references the value of X, you choose whether to double the value of X before or after that ability resolves.
2019-06-14: The copy will have the same targets as the spell or ability it's copying unless you choose new ones. You may change any number of the targets, including all of them or none of them. The new targets must be legal.
2019-06-14: Unbound Flourishing raises the value of X for permanent spells, but you don't pay any more mana.
2019-06-14: Activated abilities contain a colon. They're generally written "[Cost]: [Effect]." Some keyword abilities are activated abilities and will have a colon in their reminder text. Triggered abilities (starting with "when," "whenever," or "at") that ask a player to pay {X} aren't copied.
2019-06-14: The copy that Unbound Flourishing's ability creates is created on the stack, so it's not "cast" or "activated." Abilities that trigger when a player casts a spell or activates an ability won't trigger.
2019-06-14: If you control two Unbound Flourishings, the value of X for permanent spells will be multiplied by four. If you control three, it will be multiplied by eight, and so on. On the other hand, spells and abilities that include {X} will only be copied twice if you control two Unbound Flourishings, three times if you control three, and so on.
2019-06-14: An ability with a cost that includes X, but not the mana symbol {X}, won't be copied.
2019-06-14: Unbound Flourishing's ability will copy any instant spell, sorcery spell, or activated ability whose mana cost or activation cost contains {X}, not just one with targets.
2019-06-14: You can't choose to pay any additional costs for a copied spell. However, effects based on any additional costs that were paid for the original spell are copied as though those same costs were paid for the copy too.