Skaro Degradations

The Skaro Degradations were Dalek forces with abnormal and malformed appearances created during the Last Great Time War, which posed a greater threat than the original, unmodified species. The Degradations were created by the Daleks during experiments to retro-evolve the Dalek genome. The results created abominations of the Dalek form. The Daleks put the Degradations to use against the Time Lords during the War. Many were unstable and unpredictable. (PROSE: Engines of War)

They were described by the Tenth Doctor as one of the horrors of the Time War, along with the Nightmare Child, the Horde of Travesties, and the Army of Meanwhiles and Neverweres led by the Could've Been King. (TV: The End of Time)

Gliders
"Gliders" was the name used by Cinder and her fellow resistance fighters on Moldox to identify the type of Degradation that travelled by hovering above the ground. The Kaled mutant, resembling a limbless humanoid torso, was housed in a reinforced glass casing suspended under a regular-looking Dalek dome. They had arms and energy weapons flanking them on either side. (PROSE: Engines of War)

Spiders
"Spider" Degradations were similar in some ways to Spider Daleks. (PROSE: War of the Daleks) They were egg-shaped and moved on three spider-like legs. Their casing was red with black globes and they were armed with four energy weapons. (PROSE: Engines of War)

Temporal weapons
The "Temporal Weapons" Degradations were very similar to Special Weapons Daleks, armed with a large Temporal Cannon created by the Eternity Circle that could erase its victims from history. They were also strong enough to withstand fire from a Dalek gunstick, although it could still damage them. The War Doctor once thought these types of Daleks were not Degradations but "something new." The Daleks planned to put this new paradigm into wide use through the use of their progenitors. But the new planned paradigm was never deployed after the War Doctor and Borusa used the Tantalus Eye to stop the Daleks. (PROSE: Engines of War)

History
The Time Lords' attempt to interfere with the creation of the Daleks (TV: Genesis of the Daleks) gave the Daleks the idea to conduct further experiments on their own race. This ultimately resulted in the birth of the Skaro Degradations which were used by the Dalek Empire by the time of the Last Great Time War. They were used during the Dalek occupation of Moldox where the War Doctor encountered them. (PROSE: Engines of War)

When broke the time-lock on the War as part of Rassilon's plan for the Ultimate Sanction, the Skaro Degradations were among the horrors of the War that threatened to break through. The Doctor and the Master were able to thwart Rassilon and re-seal the time-lock. (TV: The End of Time)