Tried to make a black Path to Exile...

Eek. That's a big drawback for a big effect, so that's probably in the right ballpark, although I wouldn't like to say if it was exactly right, since balancing the drawback depends very much how much benefit your opponent is likely to get out of it. In fact, since it depends so much on judging exactly when to play it, it's a pretty interesting card.

Of course, you can also play it on your own creature, which is generally going to be better than Path to Exile on your own creature.

Oh, good point. It's a shame because I like the ingeniousness of effects you may want to legitimately play on either side's creatures, but unfortunately I think you probably shouldn't be able to because I suspect the current design guidelines say "don't design a 1-mana tutor ever, whether or not it also requires you to sacrifice a creature".

There is Diabolic Intent, but the extra versatility and instant speed (read: EOT play) over that would surely get this axed.

This is at least card disadvantage: it's a Vampiric Tutor rather than Diabolic Tutor. Interesting idea. Interesting how it's simultaneously not a good enough drawback on the removal spell and too good a version of a tutor for yourself.