Ben 10 season 3 episode 8 : Under Wraps

In order to teach Ben and Gwen the value of hard work, Grandpa Max takes them to a farm. However, a farmhand tells Ben and Gwen of a mummy that had recently arrived in a flash of purple lightning, prompting their curiosity. The two of them find it digging for a strange stone, but it attacks them as soon as they see it. XLR8 fights it to no avail, but the mummy flees in the confusion. Max discovers that the strange rock is an unstable chemical called "Corrodium," which causes severe mutation in earthly organisms. The Tennysons track the mummy down to an ice cream factory, but end up in danger when the mummy proves to be invincible. In the resulting struggle, the mummy touches the Omnitrix and inadvertently adds its DNA, allowing Ben to use that form; however, the Omnitrix decides to transform Ben into Upgrade instead. Upgrade possesses a liquid nitrogen containment tank and sprays the mummy with the chemical, effectively freezing it. The family then flees the farm for fear of more manual labor.