@creamqueen Take it to the vet, they will give it an injection or put it to sleep in a gas tent filled with nitrous oxide or atmospheric nitrogen. Its death will be painless, it will feel all pain go away, it will get lethargic and giddy, and then it will fall asleep without even realizing, and then it will die painlessly after several minutes.
@creamqueen If it was me, and my hamster was covered in tumors or the like, and killing it would be a mercy, I would put it in a bag with a base to give it structure, and the hamsters environment and some fresh fruit, and then I would poke some exhaust holes all over the bag so the pressure doesn't get high and hurt it, and I would tape a hose between the bag and a source of nitrous oxide, and I would gently turn it on until a mild breeze was coming through the vent holes indicating positive pressure, and I would observe the hamster in case anything went wrong, and I would cry.
