AU Types

AUs, as you probably know, are Alternate Universes. UnderEK is one of these. As explained here: http://undertale-au.wikia.com/wiki/Category:AU_Types by the Undertale AU Wiki, there are 6 basic types of AUs. UnderEK falls under the category of "Self insert" AUs, AUs where one or more of the characters are replaced by real people.

The AUs of UnderEK are further split into more precise AU Types. The following are the different AU Types of UnderEK.  Switch Up 

This is already an AU Type as explained by the Undertale AU Wiki:

"Some or all of the canon Undertale characters swap roles and/or personalities with the other canon Undertale characters. e.g: Sans replaces Toriel. No new characters are added, and the story is relatively the same for the most part."

Examples of Switch Up AUs are: EKSwap, Alterek and EKShift.

 EK Switch Up 

EK Switch Up AUs are similar to Switch Up AUs except it is not the roles and personalities being switched. It is the EK characters, for example: Instead of Flowey being Kyle, Flowey becomes Mike. The story also remains relatively the same; like Switch Up AUs.

Examples of EK Switch Up AUs are: True6R, Random Ed and 6RBears.

 Multiverse 

Multiverse AUs are AUs with characters, items, locations, etc that were from other Underek AUs or are still part of other Underek AUs. Multiverse AUs have a different story than regular Undertale/UnderEK or may not have a story at all.

Examples of Multiverse AUs are: gAUrdians of the EKVerse and Rejected Ed.

 Minor AU Types 

Fell AUs are AUs where everyone who is good becomes bad and everyone who is bad becomes good. The only Underek Fell AU is EKFell.

MindSwitch AUs are AUs where every character takes the personality of their EK Role instead of their Undertale character. The only MindSwitch AU is EKMindSwitch.