Before we begin, let me say that I think any sort of blue moon alternate reality event, where a normal level is remixed in some way, would be awesome. Like making a level with both fiends and gremlins or something. Here we go:

[Pre-Post: Pierce/Fire themed heavy sword would be awesome, more details at bottom under Flare Queen)

This may have been suggested already, but regardless, I think a "blue moon" alternate reality type event would be awesome. Combine this with the new buffed Shadow Lairs and it could be an awesome addition.

Essentially, all of the Shadow Lairs would be mixed and matched, such that one shadow lair would have another shadow lair's status theme. For this idea, the enemies throughout the shadow lairs would be the same monster class, but just different status. Additionally, new models for the bosses themselves would theoretically be the only new cosmetic change needed, on top of level design tweaks to match the traps to status.

Blue Moon Bosses: The Core Energy Does Strange Things

Rabid Snarbolax -> Dreadlax

- Rabid Snarbolax Lair changes to curse status theme (curse slags instead of poison slags, can keep poison wolvers), with a Skeletal-designed Snarbolax boss fight (The two Dreadlax's would be rotten/skeletal type design, and inflict curse (maybe do mixed pierce/shadow dmg).

Ice Queen -> Flare Queen

- Ice Queen changes to fire status them. The enemies throughout would be oilers instead of ice jellies, and other corresponding fire themed enemies. The boss herself would be a giant cubic flaming oiler jelly mass, to differentiate it from the giant poison oilers from Compound 42. Traps would be changes to fire traps, to set the oilers on fire.

Red Roarmulus Twins -> Chemical Twins

- Roarmulus Twins would change status from Fire to Poison, with constructs and jellies inflicting heavy poison status. The boss would be a poisoned- perhaps decaying (rusty/semi-broken down appearance) Roarmulus twins. Could make the levels overall with a more decrepit appearance.

UFSC -> Arctic FSC

- UFSC would change to freeze theme, with frost slags and frozen enemies. All enemies would inflict strong freeze to prevent immunity. The boss would be a frost vanaduke with a giant ice mace, that could inflict elemental damage. The fire patches in UFSC could remain, to provide an interesting fire/ice mix status level, or the fire patches could be replaced with frost traps.

I didn't provide too much info on the cosmetics of the levels and bosses, since the artwork can be left up to the designer's imagination. I just wanted to provide a starting concept from which a new potential event could be set.

Also, If GH wanted to add more additions, then these Blue Moon bosses could drop entirely new tokens, which could be used to purchase entirely new stuff (weapons, cosmetics, etc). Also, the blue moon lairs could provide completely different materials, that could be used to craft 4 special weapons (instead of armor sets) -> 1 bomb, gun, and sword craftable per blue moon SL?

Ideas for weapons that these 4 bosses could lead to by way of tokens/materials:

Dreadlax -> (since curse is OP, the weapons could be nerfed in some way (CTR, ASI, hit radius, range, etc) to compensate
- Curse mist bomb -> shadow damage, minor curse status
- Curse themed catalyzer (any other gun with curse theme would probably break lockdown lol) -> cursed biohazard pretty much, shadow damage
- Curse themed cutter line -> shadow damage, minor curse

Flare Queen ->
- Fire type shard bomb (Old Radiant Sun Shards mechanics?), pierce damage
- Fire themed magnus line (elemental damage, chance of fire)
- Fire themed Troika line (made of igneous rock, pierce damage heavy sword, damage reduced by 5% to compensate for minor chance of fire)

Chemical Twins ->
- Poison type blast bomb, elemental damage
- Poison type alchemer, elemental damage
- Poison themed flourish line

Arctic FSC ->
- Polar Vortex -> freeze themed vortex bomb
- Freeze themed orbitgun
- Freeze themed calibur line

The theme of this post was alternate reality event, but honestly, if the developers see even a single idea here that they can use and build off of (pierce themed heavy sword pls), then this was absolutely worth writing.