I'm unsure if the opposition will even target the pet in the first place if it's invulnerable. But I guess we'll find out once it hits the nightly. Regardless, the most "tanking" the pet can do is lure the enemy in the wrong way for a brief moment. I don't see it as an exploit so much as "comedic distraction." "Oh my gosh Stormcaller, look at that guy's adorable pet! Let's go over to it!" "Oh man Stargazer, you're right! Don't mind the fact this guy is totally attacking us!"
hell ya now we can finally have cock fights in space well you know what i mean just fights with the animal we train POPTOP I CHOOOSE YOOOOOOOOOOU
Yea, enemies don't target oblivious pets and nor deal damage to them. However, oblivious pets can actually still take damage from some other sources like lava and die.
Did you really think Tentillum was a Pokémon? It's the internal name for the felin ship pet, actually
undertale is a game with an undyne fanbase and a metaton of support its definitely a game that will last through the sans of tem