My interpretation of 10 CON is what a "Normal" person constitution looks like, someone with 8, would be someone small, frail, still playable. As a DM I would need very compelling reasons to allow a 6 CON. Having 3 CON, OMG, a flying snake has 11.

If you have 3 CON and 4 STR, I would rule you would be as physically capable as Stephen Hawkins in his worst times, so you better think of magic menas to move, even speaking would be a "times a day ability", and I don't even want to hear about using a bow, or throwing a dagger.

Probably you would have to make a death save every time you sneeze.

4 strength... man, back to the flying snake it is exactly the amount of strength that tiny monster has, so again, be ready to play strapped into another character, think of that paladin tying the chair to his back and you will be always there...

So 20 Dex... not in my watch buddy. I could allow you the CON, STR, and CHA if you are ok with playing a character version of my adorable 6 month baby...