These are in addition to the standard arcade, vs, and online
1. Tournament - where multiple players can compete, both locally and online.
2. Endurance mode - see how many enimies you can eliminate with one life bar (I really liked the endurance battles in MK1)
(See $UB-Z?R0's post)
3. Konquest - expanded with more to find and cooler missions and more koffins to unlock (MKDA had too many and MKD did not have enough)
4. puzzle kombat (I like it)
5. Chess kombat with a little different gameplay (different spells, more traps) and more options, such as the ability to do finishers at the end of a battle and the ability to play with normal chess rules.
6. Kreate - a - fighter - make your own Sujinko - any combination of fighting styles, special moves and finishers, and create your own combos - the options here are virtually limitless and would really enhance the online play.
FInally, I think there should be two options
1. The ability to wager koins in online play
2. The ability to select fighters you will fight against in arcade mode. Lets face it, in every game there are always characters that you wish were not there, wouldn't it be cool if you could ensure that you have nothing to do with these characters by not being forced to fight them in a randomly generated arcade setup.
I have not read many posts in this forum, and I am not intending to steal anyone's ideas (except I liked some of the modes $UB-Z?R0 came up with which is why I put them on this list and gave $UB-Z?R0 kredit). If I have repeated what others have said, it is purely by coincidence and I am sorry.
Let me know your thoughts.