Taru Taru no Mi

The Sakka Sakka no Mi (錯覚錯覚の実, Illusion Illusion Fruit) is a Paramecia-type Devil Fruit that allows the user to create illusions, the word "Sakka" comes from Sakkaku (錯覚) which means "illusion". It was eaten by Oz.

Strengths & Weaknesses
The main strength of this Devil Fruit is that it allows to create illusions, creating a fake reality that the user sees, such as change the appearance of people, objects or even the enviroment itself, create illusions of people or object and even create illusions of events such as death or murder, and in some cases the user can even create the deepest fears of others.

While the illusions aren't tangible, further mastery of the fruit's powers can allow the illusions to become tangible, thus making them stronger than they are before, but still unable to actually inflict any true harm, as every harm caused by the tangible illusions can't cause any physical damage but only mental damage depending on one's mental state.

Other than suffering from the usual weakness of all Devil Fruits, people who can utilize Kenbunshoku Hakito an incredible degree and even master it, can see through the illusions and know what is real and what is not, however, new illusions that would be created later on are immune to this until they are also seen through, also, the illusion isn't negated entirely, as those who aren't sufficient in Kenbunshoku Haki cannot free themselves, another known weakness is that one's mental state is also a key element into overcoming the mental damage caused by these illusions, the stronger one's personality (mentality) the weaker and less effective the mental damage is.

Trivia

 * Sakka (サッカー) literally means "soccer" making this fruits name a pun.