\begin{tikzpicture}[scale=.5, z={(.707,.3)}]
    \draw (2,3,2) -- (0,0,0) -- (4,0,0) -- (4,0,4) -- (2,3,2) 
      -- (4,0,0);
    \draw[color=gray, style=dashed] (2,3,2) -- (0,0,4) 
      -- (0,0,0);
    \draw[color=gray, style=dashed] (0,0,4) -- (4,0,4);
  \end{tikzpicture}