I am posting this to give you an innitial warning so you might prepare for it.
This is an event much like the LMS one where it will take place once a week at a certain time. It is essentially an area with a boss that will only open for 1 hour a week.
A patch for this will be released on saturday and posted on the patch thread.

Mobs drop items, players don’t but players do get pk points, players also do not break spirit sets. You will not be allowed tt’s/de’s. The NPC will be susie in BW and the levels allowed are 50+ to prevent griefing.

This is how the NPC reads:

Yimoogi Challenge is a team event. You will begin in a long
corridoor filled with monsters that you will need to fight your way
through. This coridoor will lead to a big room where a powerful
Yimoogi will be lurking. The aim is to kill Yimoogi.
Players can work together, but they can also fight each other.
Do not worry though as you will not lose any items when you die.
This event will take place on Saturday at 6pm – 7pm.