Najeela, the Blade-Blossom If you can develop some ways to get tons of any color mana, then Najeela, the Blade-Blossom is a wonderful card for attack-heavy decks: it's both one of the strongest 5-color commanders and best aggro commanders in the game
While this one only lets you dig as deep as your lands, and not twice so, it has the big advantage of coming at instant speed
They'll be in a special foil, "TARDIS Showcase" form, and each is uniquely numbered 500, plus the number of the given doctor
While the most obvious choice is to pair it with Unwinding Clock to reuse its abilities on each of your opponents turns, you can also run other clever synergies, like putting Curiosity on it for extra card draw
We're working with a single printing of every card, so even though Grizzly Bears has been printed 26 times across various sets, we only really care about one of them