Shadow-leech

Shadow-leeches are corrupted Transformers from the Marvel portion of the Generation 1 continuity family via Regeneration One.

Have you ever truly watched one feed? It is so repulsive as to be almost beautiful.

Twisted servants of the Dark Matrix creature, shadow-leeches are unrecognisable as the Transformers they once were. Through their merest touch, they can drain the life energies out of a Cybertronian and absorb them into themselves, making them deadly and nigh-unstoppable enemies.

Fiction

Regeneration One

While Rodimus Prime and his Autobots were away at the Hub Network fighting Jhiaxus and his forces, the Dark Matrix creature seized the opportunity to take control of Cybertron. The War to End All Wars, Part 4 Almost the entire population of the planet was quickly converted into shadow-leeches, with Ravage, one of the few survivors, being hunted down by a leech that used to be Soundwave, Howlback, Slugfest, Squawktalk, Beastbox, Wingthing and Overkill. At the last possible moment however, the Decepticon was rescued by Starscream and Shockwave and taken to safety aboard the Ark. King of Shadows

Upon their return, the Autobots were aghast to discover that their homeworld had been reduced to a barren wasteland and soon found themselves under attack by shadow-leeches which killed Hosehead and Slingshot. Blaster managed to corral one of these shadow-leeches in a sonic bubble long enough for Perceptor to examine it, leading to the horrifying revelation that it used to be Iguanus, and that all the leeches were former Cybertronians, transfigured into this new form along with their world. With conventional weaponry having no effect on the creatures, Rodimus sent Jetfire to fetch the Sword of Primus, but just after he departed, help arrived in the form of the Dinobots; Grimlock's prior possession by the dark entity had granted him a form of immunity against the leeches and the power to slay them, with the other Dinobots having been saved from transfiguration by their proximity to their leader. Appalled at Grimlock's willful slaughter of creatures that used to be fellow Transformers, Rodimus vowed to find another way and when Jetfire returned with the sword, Rodimus was able to use its energies to hold the leeches at bay.

Realising that the Dark Matrix creature had been masquerading as Primus and planning this for a long time, Rodimus tasked Ultra Magnus with securing the Star Chamber and dealing with Galvatron while he dealt with Galvatron's master directly in Zero Space. Without the protection awarded by the Sword of Primus, Magnus's forces soon came under shadow-leech attack once again and this time Streetwise was killed. Grimlock offered to stay behind to cover the Autobots' escape and began slaughtering shadow-leeches by the dozen. As Rodimus Prime defeated the Dark Matrix creature in Zero Space, the shadow leeches dissipated. The War to End All Wars, Part 5

Transformers who definitely became shadow-leeches

• Axer, Kick-Off and Gutcruncher were all present when the Dark Matrix creature first arose and so were most likely amongst the first to become shadow-leeches.
• Venom, Ransack, Chop Shop, Windrazor, Afterburner, Terradive, Eagle Eye, Carnivac, Snarler, Roadblock, Runamuck, Bludgeon, and Krok had all been apprehended by the Cybertronian Civil Defense or the Autobots in previous issues. If they were in custody alongside Soundwave at the time they could be assumed to have been also converted into leeches, as well as any other Decepticons to have survived the attempted invasion of Cybertron.
• Kup finds Scattershot's gun in the Star Chamber, implying that he had been converted, but he was seen amongst Rodimus's troops at the Hub Network, so either that was an error or he was absorbed by a leech off-panel after returning to Cybertron.
• In "King of Shadows" it seems that pretty much everybody's dead, Dave.

Transformers who escaped becoming shadow-leeches

† Escaped becoming shadow-leeches, but nonetheless corrupted by the Dark Matrix creature and killed on Nebulos
‡ Died very soon afterwards, as usual

• There are quite a lot of Autobots in the Star Chamber at the end; we can assume more than those listed here survived.
• The Demons escaped the shadow-leeches by entering a chrysalis-like state; later one of them regenerated into Botanica.