Your search for "Domesticated Mammoth" revealed the following:
Domesticated Mammoth - No Symbol (CMB2) from Mystery Booster Playtest Cards 2021, available at 401 Games Canada. Rarity: Rare Finish: Normal Artist: Jade Granger Card Text:CARDNAME enters the battlefield with a token copy of Pacifism attached to it.
Domesticated Mammoth - Symbol (CMB1) from Mystery Booster Playtest Cards 2019, available at 401 Games Canada. Rarity: Rare Finish: Normal Artist: Jade Granger Card Text:CARDNAME enters the battlefield with a token copy of Pacifism attached to it.