I've come around on Purple Pain a bit, it costs a lot to equip and it's competing with good moves but it does have consistent uses. A couple matchups just allow you to get away with using Amp Purple(like Jacqui) at range because of a lack of counter, and it catches people moving forward and basically gives you block pressure on any point of the screen. I've found that if I combine Pain with the projectile absorb, I can use the move more in the zoning game(would convert into combo/pressure) with some niche use of the normal version.
And then the move does have some consistent use as an oki tool. Rain gets a lot of stray hits and his insane movement gives him plenty of oki mindgames and opportunities to throw out Purple Pain. Hard to be plus enough to guarantee stuff but you backdash into Amp Purple and the opponent may have to hold it or do a hard read to counter. In this effort, I find that having the low wave is really good for enforcing oki and giving some mix, but that also further gives you reason to use meter which makes Purple Pain amp a little less appealing.
I also try it out with the move that allows air specials because it just makes him feel more complete. Air bubble charge is great for getting out of the corner.
