Whenever The Seventh Doctor attacks, choose a card in your hand. Defending player guesses whether that card's mana value is greater than the number of artifacts you control. If they guessed wrong, you may cast it without paying its mana cost. If you don't cast a spell this way, investigate. (Create a Clue token. It's an artifact with ", Sacrifice this token: Draw a card.")
The Seventh Doctor is a UW Doctor's Companion commander built around attacking to free-cast powerful spells via a guessing game. Each combat you pick a card in hand; if the defender guesses your mana value comparison wrong you cast it for free, and if not you investigate for card advantage. Manipulate your artifact count and curve to make the guess a coin flip you usually win, then pair with a companion partner to flood the board or go wide.
Free spell every combat snowballs into huge tempo and card advantage, win-win with the Clue fallback
Doctor's Companion lets you run a second partner, doubling your strategic options
Strong card advantage engine through investigate even when the guess fails
UW gives premium protection, board wipes, and evasion to keep him attacking
Effect requires connecting in combat, so removal or chump blockers neuter the whole engine
Color identity lacks ramp and reach; can stall without artifact mana
The guess can be played around by a savvy opponent if your artifact count is predictable
Five mana and combat-dependent makes it slow against fast combo decks
Free casting from the Doctor pads your life total toward a lethal blast.
Tighten the curve so your free-cast hits are consistently impactful bombs rather than filler, and add artifact ramp like Sol Ring and Treasure makers to both fix mana and warp the guess. Add evasion and protection (Rogue's Passage, Swiftfoot Boots, Teferi's Protection) so the Doctor reliably connects, and choose a companion partner whose ability compounds your engine, such as one that draws or makes tokens.
Legendary Creature — Time Lord Doctor
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