Custom Custom no Mi

[Symbiote]

@SuperSaiyan2 Challenge accepted.

Pretty simple topic, make up a devil fruit and if you see one that could be useful in the OP universe give them a thumbs up.

Kioku Kioku (Memory) no Mi
Paramecia, can alter the targets memories for a certain amount of time. The more skilled you get with it the longer you can change their memories, also effects how far back you can go.

 

[Pocket-Gog~]

Go Read Good Manga no Mi.
Paramecia, whenever the user uses this ability all fans of One Piece within a 15 mile radius will realise what a shit manga One Piece is and therefore stop reading it. A skilled user of Go Read Good Manga no Mi, will be able to convince them to go pick up the superior Hunter X Hunter after dropping One Piece.

 

[SSJ2]

Goat Goat no Mi. Ability to transform into a goat that far transcends Moro in every possible way.

 

[Captain Cadaver]

Chad Chad no Mi - Fills the user with Chad energy that allows them to erase anyone within their presence who's Haki or test level doesn't reach a certain threshold.

As for a serious answer:

Rain Rain no Mi (Would've called it Ame Ame no Mi if not for the name being wasted on some candy DF from one of the shit movies)
Logia type. Allows the user to manipulate the flow and trajectory of rain around them and any puddles recently formed by rainwater, allowing for things such as concentrating the water into a strong piercing attack akin to water cutter machines. Typical Logia intangibility also applies. In its awakened state, the user can freely change their form to that of a single rain drop if necessary and can travel between the raindrops, making attacking them directly near impossible.
Weaknesses: So that this isn't too broken, it has the drawback of only working if rainclouds are in the sky (though this can be mitigated by having some dance powder or a clima tact). Only rain water and some fresh water can be used, with sea water still affecting it as it would any DF user. The rain and its user can also be evaporated or made vulnerable to electricity, so things such as the Goro Goro no Mi, Mera Mera no Mi, the clima tact and electro users act as hard counters to it.