There aren't much of the update but to finish up the things like story and some graphics, additional with some gameplay enhance features like random enemies or you only have 1 HP and fix some bugs.
Update List
new artwork (probably final version)
improved story and event view
improved some graphics
rearrange and upgrade quality of soundtrack
change soundtrack DLC to actually soundtrack category
change some of sound effects
make normal difficulty easier
add 2 items - increase invincible time after get attacked and player has no attack delay on boss
add some of new enemies
player punch faster
all playable character now have the same stats for balance VS mode
new Master Bear's Fortress
move bossrush mode into Master Bear's Fortress
move stage select entry to the right side of base map
move new entry to stage 9-15 by get into the spaceship
steam screenshot is now working!
give rewards and abilities to modify the gameplay when player collected all the golden eggs
fixed bug leaderboards sign not working
v1.3 Multiplayer Update
CO-OP Mode
Play any stages and custom items on local up to 4 players
Versus Mode
Fight each other with mixed or any stages and custom items on local up to 4 players
Story Mode
New Items, Show Damage, Show HP
Improved some of story and character graphics (Final version of character design)
Can switch character
Bossrush give rewards on single run or full run (great money source)
Single Bossrush move to outside
Buffed light weapon
Misc
Fixed bug on stage 11 when you can fall out of map
Update v1.0.1 added cheat codes!? and some minor changes
Cheat codes
1. Go to main menu and press F1
2. Type "GIVEME30LIFES" and press enter
3. It will say "cheat GIVEME30LIFES on!!" and will hear a life up sound
This will give you 30 lifes when start new game.
I highly recommended use this when you play for first time.
It's really help you learning boss patterns without doing a whole stage again.