During the first World Martial Arts Tournamnet that Goku entered against an honourable enemy in Nam, Goku as a young 12-year-old boy invented his first technique. Remember, this was a time before any Super Saiyan transformation and flying.
Also, I’m not talking about any technique that Goku learned from someone else such as the Kamehameha Wave, as that’s Master Roshis’ technique that was passed down to Goku.
No, this technique that I’m talking about is Goku’s original new technique, which he has barley used and the first time was against Nam. Since then though, Goku has learned numerous techniques that have become iconic to Goku such as Kaioken, the Spirit Bomb, Kamehameha Wave, Fusion and Instant Transmission just to name a few.
In addition, since learning those techniques, Goku has developed his own techniques such as Goku’s God Bind, which we witnessed in the Tournamnet of Power. Flight using his tail like a helicopter was another technique that we saw only Goku use and it’s doubtful any other Saiyan needed it, as they were taught to fly early on using Ki. Therefore, it’s probably safe to say that it’s an early technique that Goku invented but not hist first.
Against Nam in episode 25 of Dragon Ball, Goku showcased his first-ever technique, which was unpredictable and almost knocked Nam out of the ring. However, it also left Goku dazed and against a stronger opponent, the technique would be useless, which is why we have barely seen it since. Also, the technique was more of a joke than an actual fighting style but it was seen again against Tien in the next tournament.
What I’m talking about is Goku’s Tornado, a technique where he spun arms out in a craze. Random erratic punches in a random unreadable direction, which almost caused Goku to pass-out from dizziness. A similar attack style was used against Oceanus Shenron and Janemba’s clones later on but Nam, as well as Tien, are the only canon opponents to experience it. This is Goku’s first technique and also probably, the most useless in his arsenal and that’s why we will likely never see it again.