Board Thread:General Discussion/@comment-28615841-20160601023944/@comment-28643257-20160603212247

Gaster is mysteryman, and a skeleton, is basically psuedo-canon now, due to his tarot card (https://i.imgur.com/HG1ELlA.jpg). it also kinda confirms that he made the DT extraction machine, due to it being in the background, and the core on the bottom.