\RequirePackage{xkeyval}

\def\@hello{Missing `hello' parameter. }
\DeclareOptionX{hello}{\edef\@hello{Defined `hello' to #1. }}

\def\@warn{}
\DeclareOptionX*{\edef\@warn{`\CurrentOption' ignored.\@warn}}

\ProcessOptionsX*

\providecommand{\scenario}{%
  \@hello%
  \@warn%
}