Oh-ho-kay, so:
1. Underworld and Hallowed are bugged as of right now. They'll be fixed in the next patch.
2. "Sand that defies gravity" is supposed to be a reference to the sandstone/hardened sand of the underground desert. Though, a lot of people seem to get confused about that, so we may change it in the future.
3. We have no cross-content as of now, but we do have plans for Thorium cross-content.
4. The erosion system is being reworked a bit in the next update, and is already quite a bit less tedious.
5. Only the Pumpkin Obelisk is obtainable as of now, so that should give you an idea on which item to use. Read through some of Erazor's dialogue to figure out how exactly you obtain it.
Hope that answers everything.
Thank you for the in-depth response! Thorium cross-content is exceptionally exciting! I'm glad Erosion is being reworked. Also, I've got a few more questions...
1. Will Midnight Rhapsody be making a return, even if just in music box form? Maybe I'm alone in this but I really liked that theme (and kind of miss The Challenger even if Erazor is a way more cohesive boss with awesome animations and even though he's H A N D S O M E as the Scavenger put it)
2. Will the Pandolar's Scavenged Items feature be moved to the Scavenger now that she's a thing? I feel like that makes more sense. I know the Pandolar is technically "Pandolar Salvager" but... I dunno. Having two scalvenaging NPCs seems odd.
3. Are there any plans for Mages to get another Relic Weapon? Melee has 6 (5 depending on dark biome), Ranged and Summon have 2, even throwing has 2!
And the Eroded Prism, while extremely cool and all, has ah... Some...
Rather major drawbacks compared to other relic weapons, so not having an alternative is a tad sad.
4. Is there any particular reason for the Pandolar in specific being so adverse to rotten eggs? I mean, obviously nobody would like Rotten Eggs, but why
just the Pandolar?
5. If the (joke?) about Niel the Cloaked Alchemist being old Challenger is canon, will we get a battle where Erazor and Niel team up for a duo-demon battle? Maybe throw Nuba in too. Big old showdown for the fun of it!
Okay that last one wasn't really serious.
Also, if I may suggest something I forgot to mention some time ago, Primordia could use a better summon recipe. Three items all dropped from a somewhat rare enemy in addition to another item which is only dropped during a semi-random event in addition to an uneven number of bars from a recipe that gives an even number is a tad annoying.
...Speaking of Primordia, her death animation has something (presumably actual-Primordia) fleeing the construct. Will she be making a return?
I may like the idea of rematching bosses a tad too much.
Oh, and on another boss-related note, heck, Araneas is terrifying. I adore how her legs are animated. It's too bad she was bugged in out multiplayer, would have been a fun boss, even though very creepy.
ANYWAY that's enough late-night rambling for now... I shouldn't be allowed near a keyboard when sleepy.