The user is altered, powered and/or created by science. Their specific physiology can be the result of scientific experiments whether proven successful or abortive, the improbable consequence of scientific accidents will. Their original physiology can be either altered through genetics (mutations), drugs, cybernetics or radioactive waste which may allow them to morph into an artificial being, one powered by scientific energies. The resulting traits and abilities vary greatly between users, can be controlled or not, and may be seen as either a gift or a curse.
Lieutenant Kurotsuchi Nemu (Bleach) is an artificial entity created from the Gigai technology and Gikon technology by Captain Kurotsuchi. The same blood flows in Nemu and Captain Kurotsuchi, hence be it interest or how to spend free time, she will have many similarities as Captain Kurotsuchi.
Cell (Dragon Ball series) is a Bio-Android created by Dr. Gero to be the perfect weapon. As such he possess the abilities of the greatest fighters to have ever inhabited or visited Earth as well the ability to absorb the energy of others in order to gain more power.
The lesser Homunculi (Fullmetal Alchemist)
Nizō Okada (Gin Tama) completely fuses with the high-tech anti-aircraft bio-weapon, Benizakura.
Sasuke Uchiha (Naruto) when he activates the Cursed Seal of Heaven.
Jūgo (Naruto) in the process of mutating himself via his enzymes.
They were being experimented by Orochimaru (Naruto).
Absalom (One Piece) after having surgical implants of different parts of animals.
Franky (One Piece) modified himself by science into cyborg, with cybernetically enhanced strength and a wide arsenal of artillery installed into his body.
Tony Tony Chopper (One Piece) in his Monster Point form.
Gatasubal (Yu Yu Hakusho) is composed entirely of a hybrid metal of combined steel and living cells, experiments of Dr. Ichigaki.
Vincent Valentine (Compilation of Final Fantasy VII) in the form of Chaos.
SOLDIERs (Final Fantasy 7) are all infused with the cells of an extraterrestrial to enhance their own physiology.
Joseph Bertrand III (Infamous) as an Infected…
…in the form of the Behemoth.
Albert Wesker (Resident Evil) after absorbing the Uroborous
Due to being experimented on with Dark Eco for two years, Jak (Jak and Daxter) can transform into "Dark Jak".
Daxter (Jak and Daxter) can transform into "Dark Daxter" due to further exposure to Dark Eco.
Sonson (Marvel vs. Capcom 2) can temporarily take on a more monstrous monkey form.
Dr. M (Sly Cooper) performed some of his gene-splicing experiments on himself to become stronger as he was easily able to grapple with Murray without showing signs of weakening. He has also survived damage capable of defeating even the strongest enemy, repeatedly, without slowing down or even showing the slightest signs of fatigue. He has been repeatedly zapped by Carmelita's Shock Pistol, bashed many times by Sly's cane, held into the air to receive many thousand bolts of electricity, and still manages to give Sly a concussion.
Richard Wilkins III (Buffy the Vampire Slayer) in the form of the snake demon Olvikan.
Xion (Bloody Roar) in the form of the Unborn.
Cadence Nash (The Troop) is a human/Blood Thrasher hybrid, and can assume her Blood Thrasher form at will.
The SA-X (Metroid Fusion) in its monster form.
Mohinder (Heroes) slowly transforms into an insect monster.
James Heller (Prototype 2)
Alex Mercer (Prototype)
Stitch, A.K.A. Experiment 626 (Lilo & Stitch), an illegal genetic experiment created by Jumba who's prime objective is to destroy anything he touches.
Experiment 624 is an illegal genetic experiment who is design to turn good experiments back to bad ones.
Shadow the Hedgehog (Sonic the Hedgehog) is the result of Gerald Robotnik's Project Shadow. Being made to be the Ultimate Lifeform, he is stronger and faster than the average being and posseses the ability to manipulate the energy of the Chaos Emeralds in order to increase his power.