Board Thread:Episode Discussions/@comment-25319479-20170426101051/@comment-25122992-20170427210034

Dude, I think you missed the part where it's shown that it wasn't an actual snake, but a snake-ending tail of the monstrous creature which silhouette has already appeared in the previous episode. So the "thing" didn't actually intervene with the summoning so that something wrong was summoned, yet the "thing" itself was summoned personally, it's the same entity all along.