Even though i dont really like this mode and would rather have a classic or mk11 style krypt+another single player mode,invasion could have been so much better but their implementation of it is awfull.
I mean for starters they should have had different types of actuall generic npcs with unique models and movsets that you fight working your way through the map,with then different types of modifires to creat novelty and challange while playing that particular mesa,and then save the actual roster characters for mini boss fights,secret encounters and boss fight of each mesa.This would actually make it feel like a mode you progress through and make the fights with roster characters feel unique and fresh.
Right now,depending on the mesa,you are fighting the same characters over and over again with near identical modifires and all of them always have super armor,with a different whacky color palatte and some random name on the health bar.It doesnt feel special or interesting fighting boss kitana at the end of the mesa if i have already fought her 50 times during the mesa haha.
Thats plus the poor reward system is what just kills this mode,if it wasnt for the scorpion skin i would not have played past the seconde mesa.