I already said a while ago that essentially every attempt at hard mode is almost a no-damage run anyway, so you're always going to be close, even if you do take a few hits along the way.
For me (as of now) this will require an enormous amount of skill + patience. Well done for those of you that have beat it on hard mode. My skill level is not that great (ex., I still can't beat MP in 2 hours or MP2 under 4) -- I hope not to go down in flames with Other M.
I know it works because I just tried it on my hard mode run. I did seem to hit more with the charge beam, but it could have just been me aiming better.
I'm wondering how you get enough time to charge and still lock on and fire fast enough with how quick his tail is during the later parts of that battle. But if it can be done, cool.
Maybe you just shoot him in the face and the spread of the Diffusion Beam hits his tail. And there's plenty of time to charge while his tail switches sides eighty times.
I just realized, Teen Ridley and Adult Ridley have exact opposite vulnerabilities. With Teen Ridley, his tail is the only thing you can hurt. With adult Ridley, his tail is the only thing you CAN'T hurt. In 2D games at least.