In my rp with my friend, we give Underfell Sans a LOT of pets. First, we gave him a cat named Luna. Then, we had them encounter a TON of Kaiju, just for the heck of it. We then had Gamera and Godzilla shrunken down and are now his pets. Finally, we had them experience the SCP Containment Facility, which introduced them to SCP 999. And honestly, who DOESN'T want him as a pet?