After you put on Simon Petrikov's crown to save your family from a family caused by the Destiny gang you would freeze everything, causing the mutogenic bomb to blow up , you see your dog Jake in a puddle of radiation and you run at him

"Don't worry Jake , I'll show you the secrets of ice" you say , as he seems to be bitting your mechanical arm

You notice he is changing and you let him in the ground as he follows you with an empty blank stare and then he mutates into the Lich