Mutate is an alternate casting cost which means youre still casting the spell, not activating an ability from your hand
Sacrifice it at the beginning of your next step
They sit on the battlefield doing their job turn after turn, and heres the part most players underrate: almost nobody runs enough enchantment removal to stop them
It was reprinted in Invasion (as a common) and later in Zendikar (again, as common) where it shined with the landfall abilities, because it was both instant and would trigger the ability twice
Does Ball Lightning preclude a Lightning Ball
They included Vanguard of Brimaz (Born of the Gods, 2014), Eternal Dominion (Saviors of Kamigawa, 2005), Pegasus Stampede (Tempest Remastered, 2015), Oubliette (Double Masters, 2020), Man-o-War (Modern Horizons, 2019), Brothers Yamazaki (Champions of Kamigawa, 2004), and Brain Freeze (Vintage Masters, 2014)