Coins: Coins can be earned when winning matches. The amount earned is determined by a few values in system.def, the current AI difficulty, and the size of both teams.
Character Unlocking: When characters are set to hidden 3, a handful of extra values can be added to slots that can make them unlockable in a few ways:
Beating Arcade Mode with a certain character
Beating Arcade Mode with a certain amount of characters
Toggling the Unlock All option in the options menu (temporary unlock)
Arcade Mode Progress Tracker: The game now keeps track of what characters, and what % of characters, have completed Arcade Mode. The % completed shows on both the main menu and the Arcade character select screen.
New Mode: All Rush Mode is just like Boss Rush, but instead of being only bosses, it's every character on the character list
Mode Locking: Boss Rush and All Rush, as well as Survival mode, can all be locked behind Arcade Mode progress.
Mod Support (sorta?): To make it easier to update Ultimate without having to add in other code afterwards, Ultimate can run code from other Lua files at certain points. These files can do things like add new text to the menus, change character names in the select screens, add new options to the options menu, and more. It even comes with an example mod! They can also easily be reloaded through the options menu.