Stradwolb
Description: they look like normal blow darts, although the faint blue glow is a little disconcerting if you have a background in nuclear physics. Yup, Cherenkov radiation! But don’t worry, that’s just a reaction from all the tachyons. There’s a small hollow section that can be used to fit a small note in.
There’s a lot of double talk about time travel and quantum entanglement and closed temporal loops involved, but the process itself is simple: you insert a stradwolb in its specially-made blowpipe, and shoot it at someone or something. When it hits, it uses up all of its stored energy to travel back in time for a variable amount; the average human being, if he blows really, really hard, can send stradwolb back about five minutes. It will reappear loosely attached to whatever or whoever it was shot at (not enough to cause damage, but enough to not immediately fall off, either).