Can't remember where I read these, but:
*) O'Sensei was once asked about "ninja" and their ability to move invisibly. O'Sensei smiled and explained that they were not invisible, but just moving very quickly and that he knew how to do it. When asked to demonstrate, he accepted... and seemed to instantly appear across the room at the door. He opened the door, smiled and said," I can be done, but it seems that each time you do this... it takes one year of your life away, so I do not use it often." Then he walked through the door and left.
*) Another O'Sensei story I have heard was from the book "Aikido Shugyo" written by Gozo Shioda Shihan. He described being an uchideshi in the home of O'Sensei. The students slept in the main room where O'Sensei had a kamiza to the "spirits" or "gods" of Aiki were enshrined. One night while sound asleep, a loud "KIAI!" was let out and all the students popped up to their feet with one turning on the lights. There at the kamiza was O'Sensei holding a bokken... and on the floor was a dead rat that appeared to have been eating the offering O'Sensei had left at the alter.
"How could you sleep and not know of this violation of the offering? I had to be awoken by the spirits and was told "Your offering is being taken by a rat." and that was happening under your very noses!"
O'Sensei was furious... the students were in shock. Needless to say, I'm sure they got busy cleaning up the mess.
*) Final Myth: Grandfather's who practice aikido are said to have the most lethal and deadly "Atemi-waza" of all aikidoka.