This achievement is very difficult. Most people will not be able to unlock this as completing the Adventure mode itself is quite challenging even without worrying about your score. The good news is that you can cheese your way through this while only being moderately competent at the game.
You will need:
-A working 360 (this method will not work via BC)
-A USB drive (the smallest size you have)
If you've done Popcap's other fan favorite Bejeweled 2, we'll be using the same method used there to backup your Endless Mode progress. Zuma's save system works just like BJ2; the save file cannot be copied via the 360's system menu and it self deletes upon starting a level and recreates the file when you manually exit to the main menu to save progress. If you don't quit to the menu properly mid-level, (dashboarding, game crashes, console is turned off) your save is wiped. We're going to circumvent all that and create restore points to fall back to in case something goes wrong. Send me a PM if you need instructions on how to do this.Strategy
Start a new game from level 1-1 and put the save file on your flash drive. Have the game install on the 360's internal memory or HDD. When you get to the point where the game starts becoming difficult, we're going to use the backup method to create checkpoints to revert to. At the start of a new level, before the balls roll out, pause and exit to the main menu, which creates the save to the flash drive. Remove the flash drive and backup your drive to your PC, then reinsert the drive and resume the level, choosing the flash drive for your storage choice when prompted. If you die, quit out and restore the checkpoint you made and try again. You'll be back to your previous state and retain all your lives.
You don't need to quit out of Zuma to do this (this is why you install it somewhere other than the flash drive), just yank the drive while in the main menu, backup, reinsert and continue. You will be doing this a LOT throughout the game depending on how good you are at Zuma. This is also why you want to use a small flash drive, since the entire drive is backed up and not just the used portion. A smaller drive will result in faster restores.
If you're struggling in the later levels, I found it helpful to make another restore point mid-way through the level as soon as you fill the bar and make the balls retract. The balls you get to shoot and special balls are all randomized as you go, so one run you can lose quickly because you don't get the right balls while the next one you can multiple bombs, rewinds, and pauses and pass the level with ease. You can make as many restore points as you need to pass the level. Don't overwrite the one you made for the start of the level in case you need to go back to it to get out of an unwinnable situation.
This means you can complete the entire game without losing a life, since any death can be undone using your restore points! The minimum score required to get 2 million on a no-death run would be 950,000. You'll have 22 lives left over (21 extra shown at the top of the screen + your current life), which are worth 50,000 each upon completing the game.But here's the best part: you don't even need to reach the 950,000!
See below for my final scores on the run that unlocked the achievement:
You can see in the images that I finished 13-1 with a final score of 1,019,920, yet I still unlocked the achievement right after popping Adventurer when I finished 13-1. I was in total shock and didn't see this coming at all. I stopped caring about lives in stage 12 when it was clear I wasn't scoring enough to make it to 950,000 so I only had 6 left at the end for a 300,000 bonus.
My theory here is that even though you're restoring to a previous game state, the code that calculates the score earned towards the Score Champion achievement adds in anything earned on your bad runs. For example, if you get stuck on level 12-4 and have to repeat it 10 times and score around 5,000 per attempt, that counts as 50,000 toward Score Champion even though it's not reflected on the in-game scoreboard. There might be more to it than that so it's possible you can finish below 2 million and still not get it. I had no expectation of this unlocking on my run and was utterly floored when I saw Score Champion come up.
Some quick notes on my run:
-I did this over multiple days and shut the 360 off each day. You do not need to have it constantly running
-I did not touch Gauntlet mode during my Adventure mode run
-I unlocked Sharp Shooter on the Xbox One midway through my run on a totally fresh install and file
-I never redid any levels, once they were completed I also proceeded to the next one
-I made a backup before the final shot on any level that had an achievement attached to it (6-6, 9-7, 12-7, and 13-1) just in case any of those did not pop. Never had any problems.
So to sum up: getting 2 million with this method will be substantially easier than doing it the intended way. And if my theory is true, then it really doesn't matter how well you do at all, because if you're like me and need multiple tries to pass the majority of the levels, you'll accumulate the score needed in the background and pop it anyway. In other words, even if you're terrible at the game you can brute force your way to the end and get this. You just have to deal with lots of tedious flash drive swapping.
If anyone else unlocks Score Champion with a total score less than 2 million please say so in the comments.