Skelecogs are types of skeleton-like Cogs that lack an outer shell, also known as the Cog Suit. Their voicesounds 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 like regular Cogs.
Thick Body: Most of the lower-leveled Cogs such as Flunkies have this body structure.
Thin Body: Many Tier 4-6 Cogs have this body type. Examples include Spin Doctors, Mover & Shakers, and Loan Sharks.
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.
Cogs have three body models and many different head models to make each Cog. Skelecogs, however, only have three models, one for each body type.
On November 21, 2014, the Skelecogs started Mega Invasions which lasted all weekend.
Another one will be happening on November 21, 2015, and will last all weekend, according to the Toontown Calendar.
Another Mega Invasion happened during the weekend on June 12, 2015.