Skelecogs are types of skeleton-like Cogs that lack an outer shell, also known as the Cog Suit. Their voices are muffed and more robotic, but still pronounce the Cog mumbles and grumbles the same way. Besides aesthetic difference, they are no different from regular Cogs and still behave and talk like regular Cogs. Unlike other special Cog types found in the game, Skelecogs are the only ones able to substitute all known regular Cogs.
Short muscular: Specifically for Cogs with a broad chested structure, but lower ranks than top tier Cogs, like Name Droppers and Two-Faces.
Tall muscular: Majority of tier 7-8 Cogs, the highest ranking and highest-leveled ones, have this body type. Examples include Minglers, Mr. Hollywoods, and Big Wigs.
As said by Doctor Surlee, the Skelecogs invading during Doomsday were a result of the fighting Toons destroying Cogs faster than they could be produced. This was also the first time Skelecogs invaded Toontown.