If you could create a Dojutsu in real life...

[ShiroShonen]

I'd rip one of the Sharingan's monikers, Tengan ("Heaven's Eye") and have a Doujutsu that can control reality and illusion at will, with no consequences.

That's a Doujutsu that trumps all others.

I'll go with this

 

[Naruto99Uzumaki]

eternal mangekyou rinnegan

 

[adeshina365]

A doujutsu will all MS and Rinnegan abilities compiled into two eyes.

 

[FemmeFatale]

Yin seal. The minds eye jutsu

 

[Bad Touch Yakushi]

Shinra Tensei always appealed to me. Also the nerve switching technique Tsunade uses on Kabuto, that'd be the perfect move in a fight, one tap and they're crippled. Victory AND humiliation.

We also unlike the narutoverse live in a world where we can see all sorts of talents and amazing things on the internet, 3 tomoe sharingan please. The copy ninja irl watching Youtube all day gaining martial arts and stuff.