documentclass[11pt]{article}
usepackage{multirow}
begin{document}
begin{table}[ht]
  caption{Partial horizontal line}
  begin{tabular}{ccc}
    hline
    multicolumn{2}{c}{multirow{2}{*}{multi-col-row}}&\
    cline{1-2}
    X1&X2&X3\
    Y1&Y2&Y3\
    hline
  end{tabular}
  label{tab:multicol}
end{table}
end{document}

documentclass[11pt]{article}
usepackage{multirow}
begin{document}
begin{table}[ht]
  caption{Partial horizontal line}
  begin{tabular}{ccc}
    hline
    multicolumn{2}{c}{multirow{2}{*}{begin{minipage}[t]{0.2textwidth}
          smallskip

          textbf{Large XX}

          here is yyyyy text
        end{minipage}
    }}&\
    cline{1-2}
    X1&X2&X3\
    Y1&Y2&Y3\
    hline
  end{tabular}
  label{tab:multicol}
end{table}
end{document}

% pdflatex mc1.tex
This is pdfTeX, Version 3.14159265-2.6-1.40.19 (TeX Live 2019/dev/Debian) (preloaded format=pdflatex)
 restricted write18 enabled.
entering extended mode
(./mc1.tex
LaTeX2e <2018-04-01> patch level 5
(/usr/share/texlive/texmf-dist/tex/latex/base/article.cls
Document Class: article 2014/09/29 v1.4h Standard LaTeX document class
(/usr/share/texlive/texmf-dist/tex/latex/base/size11.clo))
(/usr/share/texlive/texmf-dist/tex/latex/multirow/multirow.sty) (./mc1.aux)
Runaway argument?
{begin {minipage}[t]{0.2textwidth } smallskip
! Paragraph ended before @xmultirow was complete.
<to be read again>
                   par
l.15     }}
           &\