"Team TARDIS" isn't a true rules keyword—it's a creature-type-based mechanic from the DoctorWho Commander decks. Cards reference "creatures named [specific Doctor companions]" or use the partner-style rule "Doctor's companion," which lets a legendary creature with that ability pair with a legendary Time Lord Doctor as co-commanders. So your typical "Team TARDIS" deck is built around a Doctor plus a companion, giving you two commanders working together.
The nuance people miss: "Doctor's companion" only partners with a Doctor specifically (a legendary Time Lord), not just any commander, and the Doctor needs to be a legendary creature that's a Doctor. You can't pair two companions or two Doctors together this way.
In Commander, this matters for color identity—two commanders combine their colors, letting these DoctorWho decks access broader strategies built around the Doctor's signature abilities.