Yaki

To revert then the whole tail does not need to be cut off. I'd just say over half. But for the tail to be permanently gone the whole thing would have to be taken off.

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ThreeLeftsMakeARight

m.collins

Yeah it does have to be fully cut off

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Darkprince410

There's no evidence to support that the entire tail has to be cut off in order to force the transformation to reverse, as we don't see a saiya-jin's tail cut off any other length. It'd be different if we had something to compare it to, but there isn't.

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m.collins

well every time we see a tail cut off there is nothing left but tails do re grow after a certan amount of time

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Darkprince410

Yes, but just because every time that a tail is cut off, it's cut off at the base, doesn't mean that the full length of the tail needs to be cut off in order to force a regression. Secondly, sometimes a tail will re-grow after some time has passed, while other times it won't. It's assumed to be due to the Saiya-jin's age that this tends to occur, that after a certain age if a tail is severed, it will just no longer re-grow.

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Yaki

Actually I think nearly all the times that Saiya-jin tails are cut off there is a lot least a stub of tail left when they are oozaru but as they change back to normal the whole thing seems to have disappeared. Like when Bejita chopped of Gohan's tail you could clearly see a stub of tail left but when Goku turned back to normal it was completely gone and never grew back again.

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ThreeLeftsMakeARight