Kaine is a synthezoid, a synthetic duplicate of Spider-Man. Kaine possesses all the abilities of Spider-Man, he can elongate and expand his body at will, and can create tendrils and tentacles from his own body. Kaine can also drain Spider-Man's life energy with a touch. Kaine can regenerate from most injuries, and can even reattach severed body parts (although doing so causes Kaine to mutate and become less human looking). Kaine also has more control of the Spider-Slayers than Scarlet Spider, whom Kaine later fuses with the Spider-Slayers and assume a monstrous form.
In part one of The Spider-Slayers, Kaine was a part of "Project Kaine," a secret HYDRA project combining Spider-Man's DNA and Arnim Zola's synthezoids (which utilized Doctor Octopus' own agenda of creating a perfect Spider-Man). Kaine ends up making himself known when he feeds off of Spider-Man and later Spider-MJ even when they move through Doctor Octopus' secret lab, but gets sliced in half when Scarlet Spider comes into view.