TheMoon
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Developed by: Omega Force & Team Ninja
Published by: Nintendo (NA/PAL) / Koei Tecmo (Japan)
JP Title: Zelda Musou: Hyrule All-Stars
Platform: Nintendo 3DS
Release Dates: January 21, 2016 (JP) / March 24, 2015 (PAL) / March 25, 2016 (NA)
Genre: Musou-style Brawler / Territory Control Real-Time Strategy
Multiplayer: No (but there is trading for Fairy Skills for up to 4 people locally)
amiibo: Yes (Zelda-universe amiibo give character-related weapon drops, random amiibo give random loot)
New Nintendo 3DS enhanced: Yes (Stereocopic 3D support, improved framerate, C-stick for Z-target switching & camera control, ZL to lock-on)
StreetPass: Yes (StreetPass Links for Adventure Mode, was online feature on Wii U)
SpotPass: Yes (same as StreetPass)
Demo available: Yes (JP/PAL only)
DLC: Yes, see below for details
eShop download file size in blocks: 16,109 blocks (about 1.97 GB)
eManual: Official eManual PDF from NOE

A key new gameplay element is the ability to switch between the characters that are on the map currently at any point. This is new and exclusive to the 3DS version and lets you approach the whole game very differently.
Here's more thanks to Baloonatic:
A few other additions I didn't see in the OP.
- You can activate owl statues in the stages that let you warp across the battlefield quickly.
- Adventure maps are completely reworked. First map will unlock all the characters. Second map is the Great Sea which will unlock level 2 weapons for all characters and some costumes. Third map is the Master Quest map which gives you level 3 weapons and more costumes. Don't know specifics about the other two maps.
- The more characters you tell to approach a boss, the more benefits you will get. 2 characters fills your magic meter by 50% and lets you replenish magic meter by killing normal enemies, 3 characters makes the boss's weakness gauge deplete faster and 4 characters makes the boss take more damage.
- Attack animation after you deplete a boss's weakness gauge has been changed. It is much faster now.
Can't think of anything else right now. I'm really liking it though, better than the Wii U version outside of graphics. On N3DS at least.
As for a general new content overview, I'll let NOE's infographic explain:

Can I transfer saves between Wii U and 3DS versions?
No. Adventure Mode is structured completely differently in Legends and the character switching puts a different spin on story mode to make a replay feel quite different. So you're not replaying the same things the same way.
Can I get all the new Legends content on the Wii U version?
No. You can only get some of it like the characters (a download code for the Wii U version comes packed with every retail copy and is also included with digital copies, naturally). The Legend Mode content is 3DS-exclusive, as is the new gameplay element that lets you switch between characters on the field mid-mission.
My Fairy? Do I have to wear a Tingle costume to play this?
No. You can rescue fairies from keeps in Adventure Mode who will then aid you in battle. They have elemental affinities and can be leveled up. This is exclusive to the Legends version of the game and is not in the Wii U version.
Where is the multiplayer?
There is no multiplayer in this version of the game. However, you can link up locally with up to four people to trade Rental Skills for your fairy.
I don't have a New 3DS, should I buy this?
Probably not? If you can stomach low framerates and really really want to play this then go for it but know what you're getting into. There's a demo in Europe and Japan to see for yourself. Watch this DF 3DS/N3DS/Wii U framerate comparison video to get an idea.
Why is there a difference in content between the Nintendo 3DS and Wii U Season Passes?
Directly from the FAQ on NOE's website: "With Hyrule Warriors: Legends, we wanted to provide extra content that takes advantage of the game’s new features for those enjoying the new My Fairy Mode and enhanced Adventure Mode on Nintendo 3DS family systems".

This DLC overview is taken directly from Perfectly Nintendo. So huge thanks to L~A for compiling this!
http://www.perfectly-nintendo.com/h...release-planning-and-pricing-for-all-regions/
Season Pass
The Season Pass is called “Legends of Hyrule Pack”, and comes in three variants:
Nintendo 3DS Only Season Pass
Contents: all upcoming DLC for Hyrule Warriors: Legends (Nintendo 3DS) + Free The Legend of Zelda: The Wind Waker costume for Ganondorf
Release date: March 24th (Europe), March 25th (Japan, North America)
Price: £13.49 / €14.99 / 2 315 Yen + taxes / US$14.99 / CDN$21.19
Nintendo 3DS + Wii U Season Pass
Contents: all upcoming DLC for both Hyrule Warriors: Legends (Nintendo 3DS) and Hyrule Warriors (Wii U) + Free The Legend of Zelda: The Wind Waker costume for Ganondorf
Release date: March 24th (Europe), March 25th (Japan, North America)
Price: £15.29 / €16.99 / 2 778 Yen + taxes / US$19.99 / CDN$28.19
Wii U Season Pass
Contents: all upcoming DLC for Hyrule Warriors (Wii U), with the exception of the Legends Character Pack + Free The Legend of Zelda: The Wind Waker costume for Ganondorf
Release date: Summer (Europe/North America), July (Japan)
Price: £8.99 / €9.99 / 1 389 Yen + taxes / US$9.99 / CDN$14.09
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DLC Packs
Master Wind Waker Pack (DLC Pack 1) [Nintendo 3DS only]
Contents: 16 new My Fairy costume pieces, the “Master” Wind Waker map for Adventure Mode (with one new adventure battle scenario)
Release date: May 19
Price: £1.79 / €1.99 / 370 Yen + taxes / US$0.99 / CDN$1.39
More details with screenshots/artwork: http://www.perfectly-nintendo.com/hyrule-warriors-legends-screensartworks-for-the-1st-dlc-pack/
Medli [Nintendo 3DS / Wii U]
Contents: Medli
Release date:May 19
Price: Free
Notes: will be available after downloading a Software update released at the same time as the the Master Wind Waker Pack.
Link’s Awakening Pack (DLC Pack 2) [Nintendo 3DS / Wii U]
Contents: 16 new My Fairy costume pieces (3DS), 1 new map for Adventure Mode (with two new challenge battle scenarios) (3DS), 1 new playable character (Marin), 1 new weapon for Linkle
Release date: June 30
Price (3DS): £6.29 / €6.99 / 926 Yen + taxes / US$6.99 / CDN$9.89
Price (Wii U): £4.49 / €4.99 / 741 Yen + taxes / US$4.99 / CDN$7.09
Price (3DS + Wii U): £8.09 / €8.99 / 1 111 Yen + taxes / US$9.99 / CDN$14.09
Notes: if you haven’t purchased the Legend Character Pack (with the new characters from Hyrule Warriors Legends), you will get Linkle as a character, but she will only be able to use the new weapon from that DLC pack.
The Legends Character Pack (not part of the Season Pass) [Wii U]
Contents: Linkle, Skull Kid, Tetra, Toon Link, King Daphnes, Ganondorf’s trident weapon
Release date: June 30
Price: £10.79 / €11.99 / 1 852 Yen + taxes / US$12.99 / CDN$18.39
Phantom Hourglass & Spirit Tracks Pack (DLC Pack 3) [Nintendo 3DS / Wii U]
Contents:15 new My Fairy costume pieces (3DS), 1 new map for Adventure Mode (with one new adventure battle and two new challenge battle scenarios) (3DS), 1 new playable character, 1 new weapon for Toon Link
Release date: September 1
Price (3DS): £6.29 / €6.99 / 926 Yen + taxes / US$6.99 / CDN$9.89
Price (Wii U): £4.49 / €4.99 / 741 Yen + taxes / US$4.99 / CDN$7.09
Price (3DS + Wii U): £8.09 / €8.99 / 1 111 Yen + taxes / US$9.99 / CDN$14.09
Notes: if you haven’t purchased the Legend Character Pack (with the new characters from Hyrule Warriors Legends), you will get Toon Link as a character, but he will only be able to use the new weapon from that DLC pack.
A Link Between Worlds Pack (DLC Pack 4) [Nintendo 3DS / Wii U]
Contents: 15 new My Fairy Costumes (3DS), 1 new map for Adventure Mode (with one new adventure battle and two new challenge battle scenarios (3DS), 2 new playable characters
Release date: October 31 (Europe/North America) / November 1 (Japan)
Price (3DS): £6.29 / €6.99 / 926 Yen + taxes / US$6.99 / CDN$9.89
Price (Wii U): £4.49 / €4.99 / 741 Yen + taxes / US$4.99 / CDN$7.09
Price (3DS + Wii U): £8.09 / €8.99 / 1 111 Yen + taxes / US$9.99 / CDN$14.09

All screenshots taken directly from Miiverse.










Review Thread
Original Hyrule Warriors OT
DF 3DS/N3DS/Wii U framerate comparison video
amiibo trailer: https://www.youtube.com/watch?v=Jt9XxJAY1DI
Linkle trailer: https://www.youtube.com/watch?v=7FqKg_ziC-c
Tetra trailer: https://www.youtube.com/watch?v=VNd_IT9nSVs
King Daphnes trailer: https://www.youtube.com/watch?v=psvzdMNKg_w
Skull Kid trailer: https://www.youtube.com/watch?v=5XVkLm__kT4
Characters trailer: https://www.youtube.com/watch?v=fBjy7mbhK7E
latest Nintendo Direct trailer: https://www.youtube.com/watch?v=Hvmqg_TNKOk
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as usual, if you want anything added, let me know.