Technically, SSJ4 is the easiest form to defeat

[Flame Dragon]

It kinda baffles me that nobody throught about this...

But since SSJ4 is a fusion of SSJ+Oozaru and requires a tail... (unless you use blutz waves which makes your tail temporary regrow anyway)
Can't you just cut the SSJ4 tail to make him revert to base?
Kinda like Yairobe did to Vegeta.

Makes sense to me.
Especially since i believe Vegeta couldn't transform without blutz waves because he hadn't got a natural tail anymore.

Also if you cut Goku tail while he's in base form (which should be much easier considering he would be much slower)
does that mean he would not be able to go SSJ4 anymore?

[DBZGTKOSDH]

I don't think it would be so easy to cut the tail of a Super Saiyan 4. The Oozaru forms are huge, so it's easier to cut their tails, but since Super Saiyan 4 has a normal sized body, and a very powerful one, it wouldn't be so easy. Super Saiyan Grade 3 & Super Saiyan 3 are more flawed forms.

if you cut Goku tail while he's in base form (which should be much easier considering he would be much slower)
does that mean he would not be able to go SSJ4 anymore?

I guess so, since Vegeta didn't have a tail, and couldn't transform on his own.

[Legendary Saiya-Jin]

It will be about as easy as grabbing his genitals.

[TheMightyOzaru]

It isn't stated anywhere that removing the tail would make the revert to base but it's certainly possible. However if you could remove the tail you might as well remove the Saiyan's head. I don't think it's weaker than any other part of the Saiyan's body.

[DBZGTKOSDH]

However if you could remove the tail you might as well remove the Saiyan's head. I don't think it's weaker than any other part of the Saiyan's body.

The way Goku lost his tail against Grandpa Gohan, and the way Piccolo removed Gohan's tail tells me that it's easy to remove.

[Kaboom]

Being hardy or fast enough to get to a Super Saiyan 4's tail is a feat in and of itself.

[Legendary Saiya-Jin]

Oozaru Gohan was berserk and unfocused to notice Piccolo. It wasn't very easy with Oozaru Vegeta.

[NeoKING]

Can someone remind me where it was said that SSJ4 is a combination of SSJ x Ohzaru? And like it's been said, don't let GT fool you - SSJ4 is the strongest SSJ form for a reason. I doubt two SSJ4 masters such as Goku and Vegeta would let their tails get caught so easily. Also, who knows, maybe the tail becomes useless after the transformation is achieved.

[TheDevilsCorpse]

Can someone remind me where it was said that SSJ4 is a combination of SSJ x Ohzaru?

Dragon Ball Anime Illustration Collection: The Golden Warrior
Dragon Ball Back Then Vol. 3
Interview with “Dragon Ball Z” & “Dragon Ball GT” character designer Katsuyoshi Nakatsuru

The hairstyle and red fur all over the body are what really makes Super Saiyan 4 stand out.
The thought behind that hairstyle was to take it in a different direction than Super Saiyan 3, and make it wild. I made the fur red because it pretty much just seemed strong; I place a lot of importance on those sorts of impressions (laughs). Right from the planning stage images, the idea had been to bring together Oozaru Goku and Super Saiyan Goku. “Goku with primal power”, that sort of thing.

[NeoKING]

Can someone remind me where it was said that SSJ4 is a combination of SSJ x Ohzaru?

Dragon Ball Anime Illustration Collection: The Golden Warrior
Dragon Ball Back Then Vol. 3
Interview with “Dragon Ball Z” & “Dragon Ball GT” character designer Katsuyoshi Nakatsuru

The hairstyle and red fur all over the body are what really makes Super Saiyan 4 stand out.
The thought behind that hairstyle was to take it in a different direction than Super Saiyan 3, and make it wild. I made the fur red because it pretty much just seemed strong; I place a lot of importance on those sorts of impressions (laughs). Right from the planning stage images, the idea had been to bring together Oozaru Goku and Super Saiyan Goku. “Goku with primal power”, that sort of thing.

But, can't one argue that this is more in a design sense rather than an "in-story" sense? To me that sounds like - and again, this is just me, - but it sounds like they're saying, "We wanted to go radically different with SSJ4, taking it away from the 'Golden Warrior' image of SSJ1-3 and make him more Ohzaru-esque." I was referring to something like an entry in the Perfect Files that said "SSJ4 is probably sorta maybe possibly (haha, silly uncertain Dragon Ball guide book dialect) so strong because it is a combination of the SSJ and Ohzaru forms."

[Kamiccolo9]

Wasn't the tail just used to absorb the waves? After transforming, they've already absorbed them, so I'm not sure that removing the tail would automatically revert them back to base.

[GTx10]

Everybodys pretty much spot on, Goku wouldn't allow someone to cut off his tail without a fight. If someone did cut it off there is a simple solution. Head back to the Kaioshin realm and regrow it! Or rely on a Spirit Bomb to save the day. Goku literally has nothing to fear. Heck Goku could use Blutz Waves if need be!

[Bussani]

Wasn't the tail just used to absorb the waves? After transforming, they've already absorbed them, so I'm not sure that removing the tail would automatically revert them back to base.

Well, cutting it off always reverted them back from Oozaru, so it might make sense if it did the same for Super Saiyan 4. That said, Oozaru also needs a full moon, whereas Super Saiyan 4 only needed one for the initial transformation. Unless Goku transforms by generating brutz waves with his own ki or something, I suppose we could guess that Super Saiyan 4 doesn't need a moon or tail to maintain the form.