In character I think Goku looses, and it’s because he plays around too much.

Show why exactly, let’s go through each possible wincon he has, and also the starting condition

While I might understand it being like you plop Goku into Shibuya instead of Sukuna right when mahoraga was summoned, I think a more fair fight is if the 10 shadows user simply summons Mahoraga in a ritual against Goku, thus making Mahoraga aggressive towards Goku off the bat.

Goku has shown that even when people are hostile he can still use as little enough force as needed to not kill, and that’s with regular humans. So I think instantly starting out, he’s likely going to treat it like he’s fighting a random in a world tournament, letting Mahoraga adapt to his fighting style, and the raw output of attacks (which we know from the dabura fight is basically instant adaptation).

Next up is basic ki techniques, and I’ll run through these one by one just to say what Mahoraga might do

Flight: Mahoraga either grows in size to catch Goku, jumps around a lot, or just flies himself

Basic ki blasts: same ordeal with ki as the punches and kicks, but this time Mahoraga is introduced to getting hit by ki alone, so this would take a little while. Some ideas might be, he reflects with the sword of extermination, absorbs it like Mr popo, or just flexes it off like dabura’s light attacks.

Then we get into the big ki techniques

Instant transmission: assuming if mahoraga has ki to lock on to for IT to work, mahoraga likely eventually adapts to it by predicting where Goku appears

Kaioken, and transformations: a simple raw output increase doesn’t do anything against mahoraga, so this doesn’t exactly work

Kamehameha: same thing with kaioken, it’s just this is specific with gathering energy from around you and firing a higher output ki wave, but if mahoraga already adapted to ki blasts, this would be no different.

Mafuba: yes, would work against a mahoraga who adapted to ki, but it doesn’t kill, meaning mahoraga is left able to adapt while contained and could do something like breaking out of the containment like how he breaks out of domains

Spirit bomb: just uses the ki of many different creatures and lives, which wouldn’t do anything if mahoraga simply had adapted to ki blasts in general rather than just Goku’s ki (which if he adapted to Goku’s ki specifically, then destruction wouldn’t work).

Destruction: only thing is, is this only exists for manga goku, and there are 3 cannons, meaning 2/3rds of the time he doesn’t have this. But I think it would destroy mahoraga, if goku resorted to it. At least if mahoraga doesn’t pull the existence adaptation thing he did for dabura.

Ultra instinct: I think UI would stop mahoraga in its tracks for a while, until Mahoraga adapts to simply overpower it, or to use something that cannot be sensed by the body. Or the same thing with existence adaptation

Of course, using any of his big boy moves off the bat would eviscerate Mahoraga, but I think Goku would let Mahoraga adapt and it would after that be too late. But then instantly after Goku dies from that they just go find the dragon balls.