Ok, so this is a little far fetched I know, but there is actually some decent proof. To begin, there is a lot of other, more refined and provable theories I need to use to lay the foundation. In Skyward Sword, it is referenced that Demise has a tribe of demons who work for him. However, in the end of the game, when it says demise was sealed away, it doesn't actually say that the demons were also all locked away. Now, if we go on to assume that his "tribe" of demons (I believe at one point the game actually refers to them as a tribe, so there is some evidence to this connection) is the same "powerful tribe" mentioned by the Happy Mask Salesman (the tribe who used Majoras Mask for hexing rituals), and is also the same tribe of dark interlopers (the twili) mentioned in Twilight Princes, since the twili were sealed away in the twilight realm for using black magic and in MM it says there were long forgotten (because they were sealed). To prove that the Happy Mask Salesman (from now on referred to as HMS) was/is a member of the tribe, look at his knowledge and power. He has extensive knowledge of both Majoras Mask and the ancient tribe, which, using his own words, was FORGOTTEN, so if it were forgotten how would he know about it unless he was a member? He is also able to trick souls into thinking they are at rest so he can steal their power and trap it in a mask, and he makes an organ appear out of no where and disappear when he is done. Now, if the HMS is a member of the tribe of dark interlopers/demons, that means he worked for Demise. Once the incarnation of Demise's hatred was made clear, being ganondorf, he probably pledged his allegiance to him and the reason he went to get the MM was to help Ganon escape from his impending exectuion (also if HMS was a member of Demises tribe, it would explain why he would worship Ganon as Zant because it is his ancient masters reincarnation). He also appears to already know who Link is, because even though at the beginning of MM you are a deku, he recognizes it isn't your true form and that you are very courageous (he specifically says courageous), meaning that he probably already knew of Link and could tell it was him because he could sense the triforce of courage. He also says he must leave in 3 days, and that he would get MM back himself but he is to busy. The fact he knew the moon would crash in 3 days means he has some sort of greater knowledge than the average person, and it is a blatant lie that he is busy because for all 3 days he just stands there underneath the clock tower. He realizes he can just get his enemy, Link, to obtain MM for him, meaning at worst he gets the mask with little to no effort and at best Link dies trying to obtain it. On the moon, there are 4 children all wearing masks representing the four bosses you kill. Underneath the masks, you can tell they are all child versions of the HMS himself. This doesn't directly correlate to my theory, but it is just more proof he isn't as normal as he may appear. Once you beat the game, Link gives the HMS Majora's Mask. The HMS then appears to be very happy, proclaiming that all the evil has gone from the mask. Now, the HMS says he looks for powerful masks, and if all the evil were truly gone from MM, than it would no longer be powerful. If it were no longer powerful, than the HMS would have no reason to appear so happy. This means that MM still has evil in it, which HMS intends to use. Now you may be wondering, ok, but HMS looks nothing like Zant. One is a red headed human, and the other is only a little humanoid, bald, and has blue skin. Well, HMS clearly knows how to not only create but also use transformation masks. He probably killed the HMS from OoT, and used the song of healing to create a transformation mask. This would give him an excuse to be so desperately looking for MM, since he appears to be someone Link knew was obsessed with Masks. Also, In OoT, that HMS had many masks, but only one of them did anything and it was only slightly powerful. HMS in MM has many powerful masks, and he also knows the power of any mask you show him. Using the transformation mask, he disguises himself. This is also probably how he escaped being trapped in the twilight realm while all the rest of the tribe were sent there, using this disguise to not be discovered. Once he realizes that Ganon is in the twilight realm, he takes MM to the twilight realm and with its power helps restore Ganon. In the twilight realm, Majoras Mask takes on a new appearance as the fused shadow (I'm not sure why this happens, maybe they amplify its power or another reason). So all of this sounds a bit crazy, but I think a couple details make it potentially plausible. One, is that they both are seen to be incredibly bipolar, going from very happy to furious and blood thirsty within seconds. Also, they both have long necks (this isn't really important its just interesting to note). And finally, the heroes shade in TP (who is confirmed as MM Link) appears to be full of regrets. Now, from what we see in both OoT and MM, he has nothing to regret. He saves two different lands from evil, or so it appears. But, if he realizes that because of what he did, because he gave the mask to the HMS, that twilight was able to invade Hyrule and Ganon was able to reform, then I would say that is a very big regret. Because he realizes it is his fault, he seeks out a new hero to train to right the wrongs he committed. In TP, skull Kid from MM also seems to try and help the new Link, by showing him the way to the master sword. But first, he proposes a little test to Link. I think the reason is because he sees that Link (well technically Midna but they are together) has the fused shadow (which in this theory is MM) and is afraid that Link has been corrupted the way he once was corrupted by its dark power. After the test, he sees that Link does not use the evil mask to win, proving him a hero worthy of the master sword. Most theories I read seem fun, but not what was actually the intended story. However, the more I think about it, the more I think it might actually be what the developers and producers meant Zant to be. Also, since MM came before TP, and in the same timeline, it seems like the natural progression of story. Here are two pictures. The first shows the strong resemblance between the fused shadow and Majoras Mask, and the second shows concept art for Ganon in TP, revealed in the Hyrule Historia, where he has an image of (or potentially the actual) Majoras Mask on his chest. If this theory was invented by someone else, I am sorry and I didn't mean to copy you and I came up with this on my own. I know several of these theories aren't mine, but I used them to corroborate my main theory of HMS being Zant. Thoughts? TLDR: it wont actually make sense if you don't read all of the reasoning behind it, so if you aren't willing to read the whole thing then sorry.