12 was all new, not based off the ova. Which was a nice change. Tho I think his revenge was a bit more than he normally would do. But all the money the store owner made off merch based on Kid can fix the store now an his legal fees.
The witch knows who he is mostly it seems. But she lacks tact when talking with him about Kid as this one episode proved. An it looks like the series is going at least for another episode. So 13 in all. Then I wonder if later on they will switch the lead in on Detective Conan again ?
Edit hmm http://anilist.co/anime/20790/MagicKaito1412 has it at 24 episodes so if true its the lead in till spring for sure. If they was smart they would switch back an forth tween kid an http://www.animevice.com/kindaichi-case-files-returns/11-6891/ as both have given Detective Conan huge boost in ratings.