I was minding my own business in Johto safari zone hunting wild pokemon. Entei was standing there waiting to battle. I left him alone knowing I wasn't prepared. I was removed from the safari zone several times after the 20 minutes were up. When I went back into the safari zone once more, he disappeared, and he hasn't been there since. I know its not a huge deal because Legendaries aren't catchable, but for the sake my pokedex I will never have Entei entered into the data. I don't know how to resolve this.

The first time you enter that zone in Johto Safari Entei appears just to give you an hint but talking with him will not start battle. He will reappear during a quest, at the same spot :)

Oh, alright thank you. I suppose this post can be deleted.