Let me preface this post by stating that this is my first post in the ‘Ideas’ section of realmeye 
so any feedback would be appreciated, also, I will not be uploading sprites as I tried searching for a tool to and got very confused, also I am very lacking artistically. I also do not know if a similar idea has been posted, so I apologize if I am providing an already known idea.
The Idea
What if, hypothetically, there was a new arena; not the arena we know and don’t run today, but a new shiny arena that is worth running and gives new frontiers to the game?
I’m, of course, talking about Guild Run (name WIP).
How it works
A new npc is in your guild hall, his name is Neil. Neil requests 100 Mark of Bilgewater, 100 Mark of the Megamoth, 100 Mark of the Son of Arachna, 100 Mark of Oryx, 20 Mark of the Killer Bee Queen, 20 Mark of Geb, and 20 Mark of the Forgotten King. These marks may be slotted one at a time until all are with Neil, and any guild initiate or higher may give the marks to Neil. Once all marks are slotted, a guild leader or founder may activate the Guild Run. A guild run shares some characteristics of The Arena, with a few twists. In Guild Run, if you die, you lose your character just as you would outside of Guild Run. Guild Run has infinite levels just as The Arena, so doing Guild Run requires fast reaction speed as you only want to nexus in a sticky situation.
EDIT: Thanks to Kusao213 from reddit for pointing out we can use guild fame instead of marks which would indeed be much more feasibly implemented and probably much better than the marks because as Bloonmule stated, some guilds will do it within a day regardless (this was why so many marks) ALSO I will be reposting this idea with more detail and hopefully some artwork from a friend at some point. So please give more feedback so as to help me polish the final post.
(number of marks may need to be tweaked as well)
Levels 1-5
Normal Gods from the Godlands will spawn, as well as Red Demons, Lucky Ents, Lucky Djinns, Crystals, Ghost Ships, Headless Horsemen, CLand bosses, and Kage Kamis.
Levels 6-10
All above enemies ,excluding normal Gods, as well as Hermit Gods, Lord of the Lost Lands, Sphinx, and some easier dungeon bosses such as all cem bosses, Malphus, Lord Ruthven, Dr. Terrible (without invuln phase), Horrific Creation (with .4 sec vulnerability every 10 seconds), Davy Jones (with .4 sec vulnerability every 10 seconds), Septavius, and Thessal (no drowning).
Levels 11-20
All Above enemies excluding Red Demons, Lucky Ents, Lucky Djinns, Crystals, Ghost Ships, Headless Horsemen, Kage Kamis, Hermit Gods, Lord of the Lost Lands, and Sphinx.
New enemies: Killer Bee Nest, Avatar of the Forgotten King, Lost Sentry, Oryx 1, Janus, The Puppet Master, Shaitan (no movement restriction), The Puppet Master 2, Gulpord the Slimelord (Green bullets now sicken), Nightmare Colony (150 Defense, shots go in 360 degrees, skip weaken phase), Bes Nut and Geb (all spawn simultaneously).
Levels 21+
WIP
This is beginning to be a lot of lists but you get the idea, a much harder arena that you can die in.
What can I get?
Every boss/event can drop their respective white bag and has a 2X drop rate multiplier that does not stack with loot drop pots or clovers. In addition to the white bags, every 5 levels there is a test chest that will spawn in the middle of the map that may drop anything from speed/dex/wis/vit on the lower end all the way up to multiple life and mana further down the line. The test chest spawns with 100,000 HP, 0 def, and 10 seconds after being destroyed will spawn in the next wave. We could also put an exclusive UT for a new boss that always spawns at wave X.
Why should this be in the game?
Ultimately, I’ve realized that guilds don’t offer as much as one might think to the game. Sure you can run dungeons more safely and consolidate keys more easily, but once you are pretty decent at the game and have multiple 8/8s that may not matter as much to you. Furthermore there is no exclusive guild content in the game. These may be some of the reasons that I have seen so many 8/8 lone wolves lately that will sometimes pop dungeons in realm. Also there are shatters and lost halls discords that make guilds completely irrelevant for these dungeons. Furthermore, any dungeons ran in a decent guild are generally ran with an optimized plan in mind, making the runs quite static/unchanging. In contrast to this, Guild Run will be much more fluid/dynamic. Also this allows another heuristic for guild relevance/status as we can have a leaderboard for Guild Run in every Guild Hall and nexus.
Conclusion
I believe Guild Run could be an exciting and interesting aspect of the game that will prove challenging and rewarding.
Please guys, if you believe this could be an interesting idea, get in touch with me via private message and send me some sprites and more ideas as well as ways of balancing the rounds. Feedback in the comments is always appreciated.
Thanks you for reading,
Exstosator