In many ways, character progression in Mortal Kombat X is the same as Injustice. You can level a character up to 50 and you can further promote them by “fusing” them with the same character card for an even more powerful card. The max fusion level is 7, the same as the max elite level is 7 in Injustice.
Experience is gained by completing battles, either in multi-player or single-player. So far, everything is the same.
Where it begins to differ somewhat is how experience is awarded. Like Injustice, you get less experience if the difference between your character card and your opponent is too great. The drop off is less extreme than in Injustice but is made up for in other ways. Although I wasn’t watching the bronze, it appears that the amount of experience needed to level up a silver card to 50 is less than a gold. This is yet another way the game distinguishes its gold tier from the earlier game. Considering how powerful a gold card can come and how a fusion level of 7 can mean any gold card can solo through single-player it makes some sense that golds are more difficult to level up.
However, the flip side to all of that is the presence of Level-Up Cards. Unique to MKX, there are cards that level up your character and give them an equal proportion of experience at the next level. So, for example, if you have 51% of the experience you need to get to the next level, when using a level-up card it leaves you at 51% of the next level, which is quite a gain since it appears each level requires more experience to get than the last. The real value of these cards is reducing some of the grind that Injustice became notorious for. Accumulated and used at the right time and you can get your favorite card to the top levels quickly rather than endlessly grinding them. In turn, this have given me the opportunity to utilize more of my roster rather than my old standard of focusing on one card in particular to get them maxed out.
Overall, this is a relatively minor game change but a nice change all the same.