Played a game this morning that resulted in the OP having a creature with 840,000,000+ power/toughness, for sure an all time high for me. It was some Godzilla looking thing that doubled every turn (I never looked at exactly what it was) that I slapped a Sigarda's Imprissonment on. They kept bouncing my creatures but I was slowly chipping away at their life total. Sadly, in the end I did not pull the W, though I was likely a turn or two away. Game crashed, as it so often does.
::edited to cut digression
Hard to know what you're talking about with no specific info
That's simple. A green Zombie God named God-Eternal Rhonas doubles the power of each other creature you control on entering the battlefield. In past days we played that God in a loop until the power of one creature exceeded the signed long integer max number 2,147,483,647 and went negative shown as zero. Best combined with Gisa and Geralf and Primevals Glorious Rebirth. Throw in Thriss, Nantuko Primus to make them even bigger.
My guess is on Zilortha, a masterpiece card we have got in LCIxalan that paper sorta got back in Ikoria: Lair of Behemoths. "Sorta" because paper got a reskin(?) of it in the set as one of the literal Godzilla tie-ins (like Luminous Broodmoth was Mothra)... but then MTG Arena got Zilortha added as Zilortha in like one of the Anthology or PIoneer sets or something in 2023, and I don't remember if paper MTG proper has Zilortha as his own card itself. Yet.
But yes, Zilortha, Strength Incarnate has (in Puzzle Quest) "At the beginning of your turn: This creature gets +X/+X. X is this creature's power."
Hence likely how it kept growing that big facing OP. Could be fun to pair with Ziatora if she is still bugged.
I passed the signed integer value once. I posted on these forums when it happened. Some trillions of calculated damage, if I remember correctly. Fortunately, Rhonas doesn’t double their own power and was enough to actually swing for the win after the other creature powers were zeroed out