How to adjust the floating position of one figure above the other?

Question

I'd like to have one figure floating over another in a subfigure environment. Following the answers already offered here (How to put a PDF figure on top of another one), I managed to place one over the other. However, I found no clue how I could fine adjust the position of a second figure, relative or absolute position. Let's say , I rather like the Legend figure to be positioned 1cm from the right and bottom of the border of Figure 1. How could I set that?

Here is my figure structure:

\begin{figure}[ht!]
\centering
\subcaptionbox{Figure 1}{
  \includegraphics[width=0.92\linewidth]{../Figure1.pdf}}
\llap{\raisebox{20mm}{\hspace{1cm}\includegraphics[height=35mm]{../Legend.pdf}}}
  \par\medskip
\subcaptionbox{Figure 2}{
  \includegraphics[width=0.45\linewidth]{../Figure2.jpg}
  }\medskip
\subcaptionbox{Figure 3}{
  \includegraphics[width=0.45\linewidth]{../Figure3.jpg}
  }
\caption{}
\end{figure}

Answer 1

The following should achieve your goal. Note the use of % in strategic spots to avoid spurious spaces.

\documentclass{article}

\usepackage{graphicx,subcaption}

\begin{document}

\begin{figure}
  \centering
  \subcaptionbox{Figure 1}{%
    \includegraphics[width=0.92\linewidth]{example-image-a}}%
  \makebox[0pt][r]{\raisebox{1cm}{\includegraphics[height=35mm]{example-grid-100x100pt}}\hspace{1cm}}

  \medskip

  \subcaptionbox{Figure 2}{%
    \includegraphics[width=0.45\linewidth]{example-image-b}%
  }\quad
  \subcaptionbox{Figure 3}{%
    \includegraphics[width=0.45\linewidth]{example-image-c}%
  }
  \caption{A figure}
\end{figure}

\end{document}

Your use of \medskip in horizontal mode actually puts the space between the two lower images and the \caption. I've changed that to \quad.

For completeness, I've used \makebox[0pt][r] instead of \llap (they achieve the same goal though).