What's the most cards I can control at once?

Question

What's the most cards I can control at once in a game, allowing the cooperation of all players, but best if not?

A.k.a as many cards that can be affected by "X you control" effects like Serra's Blessing.

A.k.a not about the number of cards I start with or can take with me at the end of the game.

I still think it's something like Graveyard Busybody with an Abyssal Persecutor, so the opponent(s) can have all their cards in the graveyard and the game still goes on.

That gives a player control of all the cards that's possible to be played in a game.

But are there ways beyond that? Like my hypothetical "turning an infinite number of tokens into 'cards' a.k.a 'things that will persist beyond death'", is currently impossible, but are there other ways?

With everyone's cooperation, I suppose the "you own" part on something like Spawnsire of Ulamog, can be waived and just allow any kind of Eldrazi or other cards, via Artificial Evolution, to be brought in, regardless of ownership?

Without such waiving, would be best, but that's just a hope.

Answer 1

There is no limit.

Technically you can't control infinite cards, because nothing in black-bordered Magic can ever be infinite. You can have numbers that are arbitrarily large, but they must always be finite.

For example, you can set up a loop that gains you life without any limit. Copy a Leonin Relic-Warder with a Phyrexian Metamorph, have something like Soul Warden that gives you life, then target the Metamorph with its own ability over and over.

But at no point can your life total ever actually be infinite. If you actually set up this combo in a game, you can say "I'm going to do this loop 999,999,999 times" and gain 999,999,999 life, or a billion life, or a trillion, or a quadrillion, or any number you want, there's no limit on it. But it will always be a finite number.

(Is this incredibly pedantic nitpicking? Yes. But sometimes these pedantic details can matter a lot in Magic.)

So there's no limit on how many cards you can control: use some infinite mana and infinite spell recursion combination to cast Mastermind's Acquisition over and over, for example, and play every permanent card in your collection. But that number will always be finite. You can never control an infinite number of cards.

Answer 2

The limit is however many cards you have access to

There is no limit on the number of players who can play the game. A card like Admiral Beckett Brass allows for repeatable (effectively infinite) control. So how many players can you play with? How many creatures can they play with?

If you want to include "cards you own" then you can do that. In tournament settings that's limited to your 15 card sideboard.

But the answer depends on how many cards you have access to. It would seem there is no limit on that.

Cheekily, this answer previously had infinite because an infinite number of players each "donating" one card to you would give you infinite cards. But with infinite players you would never get a turn, so... you'd never get to get more cards (unless they all started to cast "donate.")

Answer 3

There is no limit.

You don't need any special card or effect, just run a deck with lots of basic lands. For example, if you want to control 1 billion cards at the same time, play a deck with 1 billion and seven swamps, and on turn 1 billion you'll be able to control 1 billion cards.