Can anything happen to a pet if I feed them any dark matter food (except the potion of course)? And while on the subject, same Q with graveyard, reborn, etc. (I'm a doof...over 15 yrs around...I know! :D)

as far as I'm aware there are no longer any items that you feed to your pet that will change them. You're safe to feed dark matter, reborn, graveyard etc. things to your pet.

There used to bottles that you filled at Peka Glade that would change your pet to a certain experiment, but a few years after the gourmand achievement came out those were all changed to give both the feed and use option and only the use option now changes your pet.

Awesome, thanks much, much, SO helpful as usual <3 <3