A whole lot of new details have come out for Splatoon thanks to a new preview by IGN.  have put a summary of the key details below for you to read, but you can also read IGN's report here:

Battle Dojo

– Battle Dojo: 1v1 offline multiplayer versus mode
– Pop balloons in Battle Dojo
– A column of colored rings indicates where a set of inflated targets will spawn
– The player with the highest score at the end of five minutes wins
– The point value doubles in the later moments of a match
– There ate special moves as a potential X factor
– Wooden crates have surprise abilities to dominate your rival
– Need to use these abilities right away
– Not all of the special moves seen in multiplayer show up in this mode
– The first player to score 30 points wins (basically a mercy rule)

amiibo

– Inkopolis has an empty amiibo box
– Scan amiibo by the container to summon one of the three characters onto the pedestal
– You’ll see a list of trials and potential rewards after scanning figures
– Get gold or amiibo-only equipment from certain missions

Divide between online/offline modes

– The shopkeepers plus their gear are a big part of the online multiplayer package
– If you’re not connected to the Internet, you cannot buy anything to customize your character
– Seems like Nintendo will send out new gear over time that provides both a unique look and useful utility
– Single-player has its own sets of gear
– Also has a separate form of currency called Power Eggs, which beefs up your gear
– Miss out on some gear if you’re playing offline
– Producer Hisashi Nogami:

“There isn’t a gear or equipment link between single-player and multiplayer. So, it’s not that you earn money in single player to then spend in multiplayer. Instead, the link is more focused on skill. You practice your controls and develop skills in single player and then you can take those with you into multiplayer.”

Other

– No custom match types with friends like Smash Bros.
– Adjust specific user settings for look sensitivity controls before or after a match