Are Toydarians immune to mind tricks?

The mind trick was said to work only on the weak-minded, and there were certain species, including Toydarians and Hutts, that were either highly resistant or immune to it.

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Also, is captain rex weak minded?

Rex is weak minded, even though he is made out to be, at least in TCW TV series, to be one of the most strong and beloved clone trooper in the entire army. Can clones mind tricked? yes. Although the clonetroopers of the Grand Army of the Republic had inhibitor chips that made them obey Order 66, it would be possible for a Jedi to utilise the Jedi mind trick.

Regarding this, can the sith use mind tricks?

In all of the films, and as far as I can think of in all of current canon, I don't think we've ever seen a Sith Lord employ a Jedi mind trick. In the old EU (e.g. KOTOR) they did so, but never in the films, and not really in the current canon that I can think. Consequently, did rex get mind tricked? He resisted a Force choke but succumbed to a mind trick when Ventress told him, "You will contact Skywalker now." Or did he? Rex isn't weak and wouldn't fall for it - he only pretended. It's a cool example of both the dark side using the mind trick and a strong-minded individual resisting it.

Then, can jedi create illusions?

A Jedi General projects an illusion of additional starships during the Clone Wars. What is Jedi mind trick? An experienced Jedi can use the Force to implant a suggestion in the minds of those they encounter, encouraging them to comply with the Jedi's wishes.