Frankenstrike has an appearance similar to the classic depiction of Boris Karloff's version of Victor Frankenstein's monster. He has a muscular body and a human nose. He has greenish-grey skin, a black mullet hairstyle with brown at the end and sideburns and 2 tower-like conductor coils on his back. Frankenstrike wears black pants with lines on them with a triangle dash in the middle that glow green. He has stitch-like lines on his arms (right arm: half of his shoulder and left arm: halfway from his glove). He has brown gloves with his fingers showing. He has 3 black and green bolts on his chest and 1 black bolt on each side of his neck, all bolts have a green line on them. He has white lines on his waist that connects it to the prototype Omnitrix , whose symbol he wears on his waist, like a belt clasp.
In Ultimate Alien, Frankenstrike's skin is completely grey. His gloves are now grey and so are his tower like wire coils. His belt is now grey and a grey hexagon is where his Omnitrix symbol used to be. The bolts are now grey and now have no green line on them. The Ultimatrix symbol replaces the top bolt in the triangular shape made by the placed bolts. The Ultimatrix symbol is now in his chest.
In Omniverse, Frankenstrike's hair is now shorter, lacking bangs and a mullet, but still has evident sideburns. His skin has several uneven seams, combining grey-brown skin with darker grey skin. He also has large pink scars across his chest and right arm. He retains the bolts on his neck, but no longer has them on his chest; instead he has one on each shoulder, elbow, and three in his back. The bolts are now bronze, and resemble a flathead screw with a green light in the crease. His belt is now green with white stripes, which have white bolts in them, and another bolt as a buckle. His turrets are now green with screws on them; the coils are now white and feature green bulbs at the tips. His gauntlets are now green with bolts on their knuckles, his legs are now a greenish-black color, and his "boots" are now copper with three green slits on them. Frankenstrike's teeth are now yellowed and uneven, and bear out when he speaks. Frankenstrike's Omnitrix symbol is embedded in the flesh of his right pectoral, with several deep scars sprouting from where it resides.