Description of feature
When a pet is wither sickened, it's still owned by the player that tamed it, and if it kills a monster, it's owner still gets credit. So, if a player is killed by a pet that was wither sickened, it should give a hidden achievement, something like "Betrayal: Get killed by your own pet"

I meant the advancement would still be given if the player used a totem to revive themselves, so hardcore players would still be able to get it.

No way to check if you’ve been damaged by a sickened pet? Or check to see if a pet was changed into its sickened variant?

this would be funny

"Et tu, brutus?" would be another name candidate

Only is issue is this goes against Hardcore

Could still work if the player was using a totem.

Interesting idea but as already brought up this advancement would lock out hardcore players which I don't want to do. I really like the idea otherwise!