The user's cells and body tissue are more powerful than the average human being's, the cells and tissues are at supernatural levels which access the entire body and just about anything connected to cells. Their entire body is modified and enhanced at the cellular or genetic level, granting superhuman capabilities.
There are at least over 75 trillion cells in the human body and more than 200 different cell types and body tissues that each work on particular functions that form the human body, including brain cells and tissues, muscle tissue, blood cells, stem cells, nerve cells, hormones, etc.
Danny Fenton (Danny Phantom) ghost powers come from his ectoplasm-infused DNA.
Saiyans such as Son Goku (Dragon Ball series) can assume the different Super Saiyan forms due to the presence of S-Cells within their bodies; the more S-Cells a Saiyan possesses, the easier it is for them to transform.
Jenova's (Final Fantasy VII) cells grant those infused with them superhuman abilities.
Shu Ouma (Guilty Crown) is a carrier of the Void Genome.
After a bag of the CPH4 accidentally broke inside Lucy (Lucy) her cells augmented to supernatural levels.
The Hulk's (Marvel Comics) gamma induced cells expand when he enters a great rage, making him that much stronger.
Hashirama Senju's (Naruto) Wood Release/Style techniques are so unique to himself that only those who have artificially implanted themselves with his cells can use them.
Mitochondria Eve (Parasite Eve) possesses supernaturally active mitochondria in her cells that grant her superhuman abilities…
…as does Aya Brea during a corneal transplant with her twin sister Maya's cornea.
Alex Mercer (Prototype) gained his powers by a lethal virus that mutated his cells.
James Heller (Prototype 2) gained the same cellular powers as Alex Mercer.
A ghoul's Kagune (Tokyo Ghoul) is entirely composed of Rc cells.
Stands Users (JoJo's Bizarre Adventure)
Toriko (Toriko) was naturally born with Gourmet Cells.
Stand Arrows (JoJo's Bizarre Adventure) were crafted from a meteorite containing a virus that grants Stand powers.
Regen Serum (Marvel Comics)
The X-Gene (Marvel Comics), the source of all mutants' powers.
Vaccine "Metroid" (Metroid Fusion)
Aya Brea’s cells (Parasite Eve)
T-Virus/Tyrant Virus (Resident Evil series)
The G-Virus/Golgotha Virus (Resident Evil series)
While it is unknown exactly how it was created and where it came from, SCP-008 - Zombie Plague (SCP Foundation) are cells that can both kill and reanimate sentient life into Zombies.
Midichlorians (Star Wars) are the source of a Force-sensitive's connection to the Force itself.
The Cells of Species 8472 (Star Trek Voyager) are the most densely packed cell structure that exists, as such they are immune to and can destroy anything that penetrates their cells- chemical, biological or technological.
The symbol of the Devil Gene (Tekken)
Rc cells (Tokyo Ghoul)
Gourmet Cells (Toriko) in both injection and pill form.
The Corvinus Strain (Underworld) is the parent strain for both the Vampire and Lycan viruses, and can also sustain and combine the two.