In One Piece, the Devil Fruit has the ability to give anyone of their special power, like the ability to prolong the body like the rubber of Monkey D. Luffy.
Here are the 10 strongest demon fruits in One Piece introduced:
10. Toshi Toshi No Mi

Recent events in Manga One Piece have revealed that the Bonney Devil Fruit can be one of the strongest demons ever.
We have seen the ability to manipulate the age of people around Bonney. However, she can also freely change her own state, allowing transforming herself into anything she can become in the future. As seen in the manga, she was able to turn into a version of the Sun God Nika.
9. Long long no mi

The Admiral of the Kizaru Navy is the owner of this demon fruit, allowing him to turn his body into light, becoming extremely agile and flexible. It also gives him the ability to shoot laser into the enemy and create a light blade to fight at close range. Obviously this is one of the most flexible and powerful evil fruits.
8. Ope Ope no Mi

Oppe no Mi is owned by Law, allowing him to create a spherical space or room (room). That place user is entitled to control the direction and position of other objects inside.
The power of this Devil Fruit allows Trafalgar Law to move instant people in the battle, creating strong shock waves and also avoiding injury by the upcoming attacks. It also has the ability to carry out an immortal procedure, by giving up his life to ensure that others can live forever. Although this has not been confirmed.
7. Nikeu Nikyu NO MI

Bartholomew Kuma's Nikyu Nikyu No Mi allows to repel anything he touches through the feet expressed in hand, including humans and objects.
This is especially useful in fighting because Kuma can make the opponent fly, counter and avoid injury by any object flying. It can also affect people's memories. Some fans doubt that it can go so far that allows Kuma to move instantly or others, manipulate souls and even erase their memories.
6. Question question no

Soru Soru no Mi gives Big Mom terrifying ability to control and manipulate the soul, as well as revive any object she chose, forming homies. Because the extraction of the soul will reduce the life of the victim and can cause death immediately, Big Mom also possesses the ability to take the life as you like.
Haki could not prevent the effects of this power even though this power could only draw the souls of those who were afraid of dying or fear of Big Mom.
5. Hie Hie NO MY

Hie Hie No Mi is owned by the former Admiral Kuzan, giving users the ability to summon, control and turn into ice at will, including stunning targets and allowing users to walk on the water.
The diverse capacity of this demon fruit makes users a formidable opponent in battle, but also useful in everyday life. Kuzan's Hie Hie No Mi was so strong that it even turned half of the Punk Hazard Island into a barren icy land.
4. Magu Magu No Mi

Water master Admiral Akainu, who is famous for his cruel personality, ate this devilish power. The power of Magu Magu not only allows Akainu to burn everything he sees, it can also make the fiery meteorite fall from the sky and prevent the enemy from coming too close.
3. GURA GURA NO MI

The Gura Gura No Mi has been used by Whitebeard, allowing users to create a strong shock wave like an earthquake, so strong that it can cause tsunami.
Throughout the series, we discovered the way white beard used our evil fruit power to completely dominate the sea, divide the Marineford Island and even create a tsunami that could destroy any army. .
2. Yami yami no mi

Blackbeard ate Yami Yami No Mi, the Devil Fruit had the power to control the darkness and manipulate gravity. As a result, he was able to absorb and disable the strength of all other devil Fruit users, dragging them into a dark space crushing everything inside, no matter how strong they were.
1. Hito Hito No Mi: Nika model

This is one of the most strange fruits of the series, because we don't know its true nature until later. Initially, everyone believed that Monkey D. Luffy owns Gomu Gomu no mi, making his body turn into rubber.
But the truth reveals its correct name is Hito Hito No Mi: Nika model. This demon fruit gives Luffy the shape and power of the ancient sun god named Nika. He has full freedom of his body and can control the surrounding environment.