So a character with 3STR gets -4STR from Stinking Drunk and has the Crown Regent token. Can the character attack on a power a challenge? Or does the character need another character in battle for the Crown Regent to add to the total STR?
Multi
from the core set rules
If you choose this title, you
add 3 to your side’s total STR
in any pow challenge in which
you have at least one participating
character.
So you don't need to have a character with str. You just need to have a character.
And by the way, if a character's strength is negative after all modifiers are applied, you round its strength up to 0, so with the Crown Regent title you will count 3 total strength for the challenge.