What it does
"Impossible Girl" isn't an official Magic keyword or ability—it's a creature subtype/character reference rather than a rules term. You're likely thinking of Clara Oswald, the "Impossible Girl" from Doctor Who, who appears in the Doctor Who Universes Beyond Commander set. Cards like her are companions, designed to pair with Doctor commanders under the partner-style "Doctor's companion" mechanic.
The rules nuance: "Doctor's companion" lets you have a legendary Time Lord Doctor and a creature with "Doctor's companion" both as your commanders, similar to Partner. People often confuse this with the separate "Companion" mechanic (Ikoria sideboard cards)—they're entirely different.
In Commander, this matters for deckbuilding: you build around the Doctor/companion pairing for two color identities and synergy, especially with time counters and "saga"-style effects common in that set.
Iconic cards with Impossible Girl
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