 Zacian, Zamazenta, and Eternatus are the only Pokémon that cannot Dynamax.Eternamax (ムゲンダイマックス "Mugendaimax") is a mechanic introduced in "Pokémon Sword" and "Shield", exclusive to the Legendary Pokémon Eternatus.Eternatus changes into its Eternamax form after defeating it for the first time.