No idea if you can play it in Challenge. I don't think it works that way.

well that's upsetting.  

I'm not entirely sure either how it works, but I've done something like 20 dark notes so far, and I have over 20,000 rhythmia.  None of those dark notes unlocked any new songs, but they do get me shards that seem to unlock characters.  With 20,000 rhythmia, I have three songs unlocked in Challenge mode, so maybe that's the only way to do it.  Series seems to be the fastest way to get rhythmia, too.

Loving the game so far. However, I'm not seeing as much DLC available (only bought Cosmo Canyon - FFVII) as some have mentioned. Perhaps because I'm in Canada?

If there's 8, that's the amount supposed to be there.  They update with more DLC later, though I'm not sure when.

Okay. That's what there is. Thanks.

it's funny, as a game reviewer it's my job to understand the subtleties of games and pick up the finer details of even the most out there games, a task I'm usually able to grasp with ease, but for the life of me I'm just not understanding this game!

How do you unlock characters?
What ARE dark notes? I keep going through them, but what do they DO? What is their significance?
how do I play multiplayer?
What do items and abilities actually DO? (I haven't equipped any yet)
How does one unlock all the enemies and bosses in Chaos shrine mode?
For that matter, does it matter if you kill the boss at the end of each battle mode?

so many unanswered questions!

But then again, I did just unlock an awesome song while I was waiting. When it does so, it can be played in challenge mode under "Encore", which is between XIII and I. it was Dancing Mad, and I got it just as I beat the game (got 10 000 rhythmia)

Characters are unlocked from collecting the shards from Chaos Shrine and Rhythmia.  Dark Notes are two songs bundled together randomly (I am not sure but I think the notes are also arranged differently in some of them than the ones you can find in challenge) one being a field music, the other being battle.  

You play the multiplayer in Chaos Shrine, and haven't seen anywhere else.  It's local.  Items can do things like cure you and give you some abilities or boost your stats.  Abilities do  various things like heal your HP bar, increase your HP bar, increase your strength (beating the monsters in the battle mode become easier for trophies and more items), special attacks, and more.  

Don't know about how to unlock monsters and bosses in Chaos Shrine, but maybe you just need to play them over again. 

Bosses are more likely to carry special items or the shards that unlock characters.  Get more rhythmia for more Encore songs.

I was able to gather most of that from my reading the game's tutorials, I just haven't seen any of it in action.  

For example, I found bahamut magicite, can I use bahamut by equipping it on my party leader?  

What do stats do?  I recall the game DID explain them to me during the tutorial, but I've noticed absolutely no effect on my gameplay whatsoever.  Cloud, for instance, has much higher HP than anyone else in my party, yet he doesn't seem to last any longer.  all these stats, abilities, equips, and collectibles don't seem to have any effects on my gameplay whatsoever, and therein lies my confusion.  I know I HAVE these abilities, but how do I USE them?  what is the point of levelling up?  

Also, is it just me or in chaos shrine, does the song difficulty fluctuate between expert and ultimate?  I look down at the timeline bar and notice there are different colors that seem to coincide with how challenging a particular portion is.  just wondering if the chaos shrine is all about mixing it up that way or not.  

I'm not entirely sure but I think the HP thing is only for your leader.  I can't be too sure, though.  The RPG elements don't do a whole lot for the gameplay itself, but it can be fun to play around with.  

Using your abilities isn't something you control directly.  Some of the skills say it has a % chance to work something like half way through the song or it goes into effect whenever you get a certain length in combo.  

Agility is used for the field so you have a better chance to encounter a moogle, and I think it gives you an item.  As for teh chaos shrine, I really don't know for sure.