1> The puppet kid is a spy for Angel, isn't he? In an early episode, Shura commented about not being the only spy Angel had sent to True Cross. We don't know what or who he really is, though. I like to imagine that he's the archangel Uriel who's working with the Vatican.2> Not sure. They had a key, but I don't understand how that would help them from inside a ball of foliage.
I assumed that Egin (the grandfather) had resurrected the Polish teacher's wife. Egin was willing to use tools that others would consider immoral (as in, the bomb to destroy the holy world and those hideously cursed weapons that were passed out to the exorcists), and he would have had time to find the artificial life facility.3> Satan is an immortal. Maybe he could be obliterated, but destroying the gate that he was possessing wouldn't destroy him. And he didn't really give up; he was defeated.4> Mephisto's Ultimate Goal: Making sure that life isn't easy for anyone?This show is a B+ for me. It's not perfect, but it is fun, contains fascinating characters, is beautifully drawn as a whole, and bravely incorporates religious and literature references that (I assume) are completely unknown by most of its primary target audience and are rarely considered by its expanded audiences.I can forgive that important aspects of the show are left to the imagination, because that's typical in Japanese animation. Anyway, the movie might explain more.   See 5 other replies

1) its implied that puppet kid is a spy from gehenna, although its unclear if he works for satan or mephisto or some other person. 2) noihaus (or neuhaus) is still around. we don't really know who brought the wife back to life. its implied that it might be igor (the husband), or someone who wanted to frame him for continuing artificial life research and have him eliminated for it. but its filler material, so i wouldn't worry about it too much.3) i think we can safely assume that satan's still alive in gehenna and has only been temporarily defeated because the artificial gate was closed. as they say in the epilogue, he'll be back. also, remembering that this is filler, at the end of all filler arcs they reset to the "staus quo."4) one of mephisto's stated goals was to train up rin. he's said it several times. we don't know why though, and he does appear to have some ulterior motives. mephisto is hedonism and corruption - he's heavily based on goethe's mephisto. therefore, unsurprisingly, the soliloquy at the end only makes sense if you've read goethe's "faust". if you haven't you should, its a good read. i thought the ending was rushed as well - i don't know if it's poor planning, or long-term plans for the show were changed at the last minute, or what exactly.   See 5 other replies