Find a way to freeze Doctor Voodoo during Free Play in any area of the game.
Doctor Voodoo is included with the ‘All-New All-Different Doctor Strange’ level. You will also need a variant of Loki for his ice beam ability. When you are in any level in Free Play or in any hub (most of which are accessible after completing the level ‘Earth’s Mightiest’ in the main game), select Doctor Voodoo as your character. Then switch characters and select Loki as your other character. As Loki, hold to aim at Doctor Voodoo and shoot him with your ice beam to freeze him, unlocking the achievement.