Devastator

In Quadrant mode, Morphs are triggered by shooting the blue squares with a plus sign (see trophy icon) - this reveals a large purple dot. If you fligh into the dot, a section of the level with transform. These squares respawn constantly, and there are usually 4 on the screen at any given time. You will be able to perform multiple Morphs in each run of Quadrant, but probably will need a few games to get 50 total. This isn't tracked, but shouldn't take more than a handful of runs.

Note also that you will need to do 10 Morphs in one run for Quadrant Master