Nice.
I've been playing around with an idea lately, after several modifications I've found the best way i think.
Contrast:
Rather than collecting blocks to score you have to avoid them, kinda like Mono with only greys.
The scoring system would exactly work like the scoring system now for the Mono except to build up points you need to avoid blocks. The block display would fill up depending which lane held the block that you've avoided*.
Hitting a block would cause your ship to become a ghost for 4 seconds and your avoidances would not count for that time, you still have to avoid the blocks though because if you hit one than your ghost penalty timer will reset; if you had a combo building up when hitting a block than it would either finish instantly (if you have the Phaseback power on cd, see below) or if Phaseback is off the cd than you'd get two seconds to dispel the ghost and continue your combo.
*(For example: If you've avoided a block that was in the left lane than you would start to fill the left column.)
Powers:
Autopilot - For 3 seconds your ship automatically avoids all blocks using the best course, this can cause an overfill because the autopilot doesn't pay attention to the current status of your block display.
Cooldown: 25 seconds.
Phaseback - If you are a ghost while using this power than you can dispel your ghost penalty that you get for picking up a block, if you are quick enough than you can even continue your combo. However if you use this power while in normal mode than you can pick up blocks for two seconds (overfill rules apply).
Cooldown: 20 seconds.
Shoulders:
Casual - Yes
Pro and Elite - No
Overfill penalty:
Casual - None
Pro - 2 second ghost (cannot be dispelled)
Elite - 2 second stun (you will get locked into your current lane, if you pick up more than one block than the ghost penalty timer will reset for each one, you can't use Phaseback while stunned but you can use it after the stun ends)
Ironmode rules would stay the same like they are now.
Hmm i hope all this makes sense, I'm a bit tired

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Keep up the good work with Audiosurf, it's a very good game and nice change from the spam of soulless games these days.