Sasuke can't use tsukuyomi in the first place
Sasuke doesnt have tsukuyomi
He does.
Sasuke, Madara and (I think) obito all have tsukuyomi. Tsukuyomi comes with the left MS that's what i think obito was using on kakashi in the dream world in the first place, and what he used to kill konan etc.
The thing is, though all those guys can use tsukuyomi, Itachi is the only one among them with an advanced tsukuyomi. Itachi can perform nature manipulation(i'd assume that's wtf is going on) on his tsukuyomi to alter time and matter in tsukuyomi, making his tsukuyomi and specialist version.
That is, Itachi has a specialist tsukuyomi, sasuke has a specialist amaterasu, and madara has a specialist Susano'o.
Obito's Kamui is still unconfirmed as to what kind of MS ability that could possibly be - maybe it's an advanced form of genjutsu which allows for S/T, similar to how izanagi breaks the very fabric of reality.
Shishui's KA is potentially anotheer specialist form of tsukuyomi.
Tsukuyomi is pretty much advanced sharingan genjutsu performed with the MS.
EDIT: The higher leveled sharingan you get(1 tomoe, 2 tomoe, 3T, ms, EMS, rinnegan?), the stronger your sharingan abilities become.
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