The soft edge option on the eraser is great, but a transparency option, I would say, is an absolute MUST for an animation app.
You really need to be able to sketch and then take back (partially erase) a drawing before sketching over and finessing the lines. Often, the sketching and taking back can go on for several iterations before a drawing is ready.
Currently this can be done by using the onion skin feature and moving back and forth between two frames, but being able to take back a drawing with a 50% transparent soft eraser would be so much better.
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