The Seventh Doctor

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 "{2}, Sacrifice this token: Draw a card.")

Ace, Fearless Rebel

Nitro-9 — Whenever Ace attacks, you may sacrifice an artifact. When you do, put a +1/+1 counter on Ace, then it fights up to one target creature defending player controls.
Doctor's companion (You can have two commanders if the other is the Doctor.)

Academy Manufactor

If you would create a Clue, Food, or Treasure token, instead create one of each.