The Yetmmud are a possible species from the second Realm.
These creatures leak from their Reality to ours. Often, the resulting damage leaves behind a portal to an unknown dimension. The effects can not be predicted, as they are absolutely random, meaning, they follow more than an infinite number of rules.
There have been 471 recorded cases, of which, their size ranges anywhere from -800 octillion yottaparsecs to:
Their duration of stay also varies, from -6 hours to 17 hours.
The damage of their visit is variable. The least damage done was nothing, the most, event EV5/5-23.
A Yetmmud entered our Reality and performed a █████ of ██████, The damage resulted in 71 novemseptuagntillion dimensions being corrupted permanently, leaking into other verses and corrupting their data. ~500 deities died in battle. Damages were irreparable and an estimated 300,000 dimensions had to be deleted eternally.
This event is often nicknamed the Cataclysm of 45, due to the fact that it happened in the year 45 in the OYC (Omniversal Year Calendar), and is mourned annually.